Portable Document Format
|Portable Document Format (PDF)|
|File extension :||
|MIME type :||application / pdf|
|Magic number :|
|Developed by:||PDF Association|
|Initial release:||1993 by Adobe Inc.|
|Current version:||2.0 (as of July 2017)|
|Standard (s) :||ISO 32000 , Adobe: PDF Reference (for 1.7 and older)|
The Portable Document Format (English; PDF for short ; German: (transport) portable document format ) is a platform-independent file format that was developed and published in 1993 by Adobe Inc. and is currently being further developed by the PDF Association .
The aim was to create a file format for electronic documents so that they can be reproduced true to the original regardless of the original application program, operating system or hardware platform. The goal was achieved and is reflected in the ISO 32000 series of standards (ISO 15930 for PDF / X ). For this purpose, the functionality of the PostScript format was essentially used. A reader of a PDF file should always be able to view and print out the document in the form specified by the author. The typical conversion problems (such as changed page breaks or incorrect fonts) when exchanging a document between different programs are thus eliminated.
In December 2019, however, researchers from the Ruhr University Bochum and the IT security company Hackmanit published that it is possible to make changes to signed and encrypted PDF documents with a simple text editor without most PDF readers noticing.
In addition to text, images and graphics, a PDF file can also contain aids that facilitate navigation within the document. This includes, for example, clickable tables of contents and miniaturized page previews.
Basics and software
PDF documents and files can be created from texts , images and graphics - mixed or individually - with the appropriate programs (e.g. with free programs such as PDFCreator and office packages LibreOffice / OpenOffice.org , fee-based programs such as Adobe Acrobat or simply via the Print dialog) and display it with appropriate reading programs (e.g. Evince , Ghostscript , Okular , Adobe Reader , Foxit , Preview ). The creator of a PDF file can protect it from unintentional use in a variety of ways by activating the PDF security mechanisms. By encrypting the access to unauthorized persons is prevented. Depending on your needs, opening the file may already require a password, or copying content from the file or printing may not be permitted. However, the protective mechanisms implemented in PDF for this are not reliable; in particular, simpler forms of encryption are easy to overcome.
In the start-up phase, Adobe Reader was chargeable. It was only the free distribution of the software that made it possible to spread the format to the extent it is today. PDF has long been a commercial ( proprietary ) but open file format documented in Adobe's PDF Reference Manual. Adobe introduced it to the ISO standardization process at the beginning of 2007 and with its publication on July 1, 2008, PDF version 1.7 as ISO 32000-1: 2008 is an open standard .
Certain methods when dealing with PDF were standardized by the ISO beforehand to facilitate data exchange in prepress (as PDF / X ) and for long-term archiving of PDF files (as PDF / A -1 in ISO 19005-1: 2005).
Generation and Transformation
PDF is a vector-based page description language that allows the display to be freely scalable. PDF files describe the layout created with the creation application proportionally in a form that is independent of the printer and the default settings , and therefore as true to the original as is possible in principle. This is where the PDF differs significantly from advanced description and markup languages such as SGML or HTML when it comes to the requirement for optimal layout fidelity. In order to optimize a display on output devices with a small display area - such as PDAs or mobile phones - markups (similar to HTML tags) can be stored in a PDF, which allow the page contents to be broken up - then inevitably with restricted layout fidelity. Such markups also enable a reader program to read the document to visually impaired users and make it easier to convert the content to other formats.
A popular application for creating PDF files is Adobe Acrobat Distiller , which creates PDFs from PostScript files. Acrobat Distiller is available as a desktop product for Windows and Mac OS. Server versions and the free Adobe Reader also exist for other platforms. With the help of the free software Wine , Acrobat Distiller also runs under Linux. Various office and DTP programs from other manufacturers offer direct PDF export and are available on a number of platforms . Now with numerous tools and programming libraries, PDF files can be created in various ways with different specializations. PDF files can be created on almost any platform.
Adobe partially grants developers the right to develop their own applications for generating and editing PDF documents, but reserves the copyright for the specifications. PDF as a page description language can be viewed as a further development of the PostScript graphic model, which is also disclosed. At the end of February 2007, Adobe announced that it would incorporate version 1.7 of the PDF specification into the ISO standardization and is working with the American industry association AIIM , which holds the secretariat of the ISO committee TC 171. Adobe threatened Microsoft with antitrust lawsuits if the open PDF standard was integrated.
Further generation methods are covered under Converting Other Formats to PDF .
Use and properties
A PDF file can accurately reproduce documents including all colors, raster and vector graphics , as well as fonts . One of the strengths of PDF is that there are display programs for all common platforms so that the content can be displayed regardless of the platform.
Subsequent editing of PDF files is difficult. However, there are different programs with which you can cut out individual pages and change certain content. From Microsoft Word version 2013, PDF files can be converted into Word files directly in the program.
Scope of documents
PDF documents can contain several hundred thousand pages. The page size is not limited by the format itself. In Adobe Acrobat, however, there are implementation limitations:
- up to version 3 to 45 inches × 45 inches (1.143 m × 1.143 m)
- up to version 6 to 200 inches × 200 inches (5.08 m × 5.08 m)
- from version 7 to 15,000,000 inches × 15,000,000 inches (381 km × 381 km)
Storage of information in the document
In PDF files, all information is saved as numbered objects. Objects are, for example, font information, character widths, character encodings used (Mac / PC ...), page descriptions, parameters for decoders, crop boxes, individual bookmarks, color definitions, page orders, bitmaps, forms, jump labels and everything else that is saved in PDF files can be. A hundred-page PDF file can easily contain 10,000 objects.
Fonts (with the exception of pixel fonts) and vector graphics can be enlarged as desired without loss of quality. Under these conditions, large network plans and data models can be stored on a PDF page without loss.
Text passages, tables and graphics (including excerpts thereof) from PDF documents can easily be further processed in other application programs by copying and pasting the respective elements, if the creator of the document has given permission. Text can be extracted not only for further processing in other applications, but also for browsing or for use with other output media such as screen readers . Detailed content can be found very easily using the text search in individual documents or full-text research within a PDF document collection. This even works if the text is graphically distorted, for example in the form of a circle or curve.
Encryption of PDF documents
A special feature of PDF is the optional document protection with 40 or 128 bit encryption . By assigning a user password, it is possible to make the document accessible only to a limited group of people. The author can also use a separate owner password to specifically assign rights to the relevant document. This prevents users from changing, printing or copying part of the document. Even without knowing the owner password, however, these rights restrictions can be easily removed with the help of various tools, especially if an owner password is used but no password is required to open the document (this means that no user password is set). The usage restrictions associated with encryption can easily be bypassed by saving screenshots as bitmaps and then using optical text recognition .
Appropriate tools can also be used to assign rights that make it possible to add notes, comments and file attachments to PDF documents or to save form entries. Originally, these features could only be used with Adobe Acrobat, but from version 7 it is also possible with the free Adobe Reader to add notes and comments and to fill out interactive form fields, provided the relevant document has been given the necessary authorizations by the author.
Vulnerabilities caused by human error
PDF files can inadvertently contain confidential information that is not immediately visible but can be found using text searches. On the one hand, information can be obscured by objects or located outside the page display area, on the other hand, a PDF can contain metadata that is only displayed when the corresponding dialogs are called up and sometimes goes unnoticed. In particular when "blacking out" text passages, it is not sufficient to cover the respective text passage, but it must be completely removed from the PDF. It is not always easy to avoid unwanted information in a PDF, especially not if you have not only created and edited the PDF (and the document from which it was generated) yourself. It is important that when redacting text passages, a tool is used that completely removes the relevant content. It is just as important to check the metadata (to be found in Acrobat via File / Properties). Acrobat Professional 8 offers extensive support here, in particular through a special function for removing hidden information.
- A file dealing with the death of Italian agent Nicola Calipari , who released journalist Giuliana Sgrena from Iraqi hostage in March 2005 . US soldiers shot him shortly after this action. The published report was censored. However, the editorial revisions were found in the published file by copying the text and saving it in a new file.
- The White House in Washington published George W. Bush's speech on the "Plan for Victory in Iraq." The file details disclosed the ghostwriter , namely Peter Feaver , professor of political science at Duke University in North Carolina , who has been advising the National Security Council since June 2005 .
- After the attack on the vehicle convoy of the Lebanese politician Rafiq Hariri , the previously deleted references to the names of Syrian officials who were suspected of being responsible for the attack were found in a publicly published PDF by the UN (see Mehlis report ).
- In 2007, as part of the Formula 1 espionage affair, confidential data about the Scuderia Ferrari car came to the public after its central technical values were only marked with a black bar in a PDF document that served as evidence, but the text was still was present and extractable.
Easily hack encrypted or signed PDF documents
In December 2019, researchers from the Ruhr University Bochum and the IT security company Hackmanit published that it was easily possible to make changes to signed PDF documents without 21 out of 22 PDF readers noticing. The Adobe Acrobat Reader did not mark subsequent changes either. The evidence was presented at the Chaos Communication Congress in Leipzig from December 27 to 30, 2019. The researchers showed that it was possible to (a) add pages and notes to signed documents without invalidating the signature, (b) move originally signed content to a different position in the document and write something else in the original place, and (c) to change (“manipulate”) the metadata of the signature. The affected PDF readers did not recognize the change and still indicated that the signature was valid. The researchers were able to make the changes using a simple text editor.
The researchers were also able to easily make changes in encrypted PDF documents. Even without knowing the password, they were able to incorporate hidden commands in the role of an attacker. If the attacker forwards it to the actual recipient and types in the password, the attacker has automated access to the complete decrypted PDF content. This was possible using two methods. The first method takes advantage of the feature that allows PDF files to be partially encrypted. Among other things, the structure of the PDF can be changed and non-encrypted content can be added. As soon as the document is opened by an authorized person, the attacker can extract the plain text and thus gain access to the content. The second method is based on a vulnerability in the PDF encryption specifications. This allows encrypted content to be changed. 27 PDF readers were examined for encryption. All tested PDF readers were susceptible to one of these manipulations. The ISO standard does not contain any clear guidelines for developers on how they should implement digital signatures and encryption (as of January 2020). In order to achieve a reliable signature and encryption of PDFs with all PDF readers in the future, it is necessary for the ISO to further develop the standard.
Editing of documents
PDF was designed as an exchange format for finished documents. There are now a number of programs and extensions for Adobe Acrobat that can be used to edit PDF files. However, the format cannot be compared to the file formats of word processing programs or graphics programs and, apart from the note and comment function, is only suitable for further processing of documents to a limited extent. However, within certain limits it is possible to remove typing errors , for example . The advantages of desktop publishing for graphic artists and designers are the integration of all elements for printing.
Depending on the individual case, PDF documents can be either larger or smaller than the files of the original application. The size of a document depends on the type of data it contains, the efficiency of the creation program, and whether fonts have been embedded. Fonts can either be embedded completely, as a subset of the characters actually used in the document, or not at all. If a document is to be displayed reliably, regardless of whether the fonts used are installed on the target platform, at least the characters actually used must be embedded.
Printing in batch mode from the command line
Printing is usually done within a viewer's graphical user interface with File ▸ Print… . Acrobat Reader and Foxit Reader have partially removed the command line option / t <file> <printer name> in the newer versions (September 2015). In Acrobat you can only print on the default printer, whereas with Foxit the printer can be selected, but Foxit opens the application window and does not close it after printing (the user has to close it manually).
About CUPS :
lpr -P <Druckername> "datei.pdf"
Batch printing is possible with Ghostscript . Ghostscript installs itself with the help of an installer under c: \ Program Files \ gs \ gs <Version> \ . There are executable files in the bin \ subdirectory . Example with the DOS window in Windows 7:
C:\Program Files\gs\gs9.16\bin>gswin64c.exe \ -dNOPAGEPROMPT \ -dNOPROMPT \ -dNOPAUSE \ -dBATCH \ [-dDEVICEWIDTHPOINTS=<Number of American points for the paper size>] \ [-dDEVICEHEIGHTPOINTS=<Number of American points for the paper size>] \ -sOutputFile="%printer%\\<server>\<printer name>" \ -sDEVICE=mswinpr2 \ <myfile.pdf>
gswin64c.exe is the 64-bit version without a separate window with interactive mode on the command line.
dNOoptions switch off the interactive mode. The
-dDEVICEoptions can be used if the printer uses an unusual paper format.
-sOutputFileindicates the name of the printer.
-sDEVICErefers to an internal module of Ghostscript, which is
mswinpr2a default setting. At the end the command line expects the file to be printed (can fail if the order is different). During printing, a cancel dialog appears which closes itself (can be switched off with
Ghostscript for Windows also displays the PDF file in its own graphic window if there are no command line parameters. This display shows pixels and staircase effects. In contrast, the quality of the printed documents is significantly better.
Serialization and Compression
In the course of its development, PDF was adapted several times to special requirements for use on the Internet . Originally, a document had to be completely available in order to be displayed. It is now possible to serialize PDF documents so that parts of them can be displayed while they are being loaded. From version 1.5 of the PDF specification , several objects can be combined in one PDF and then compressed, which leads to significantly better compression, especially with the numerous small objects required for the document structure (image data or the actual description of a page has always been compressed) .
When archiving printed documents as PDF files, a mixed approach is preferred in order to both preserve the original document as much as possible and to ensure searchability. By cleverly combining the image compression methods supported by PDF, a very strong compression is achieved (typically 1: 200) by compressing the background (typically flat structures and color gradients) and text (sharp edges, but only a few colors) with different, specially suitable methods and then placed on top of each other. The actual text is extracted using the OCR process and embedded invisibly.
In contrast to previous page description languages such as PostScript, the "preview" on the screen is no longer just an aid to avoid test printouts, but offers convenient functions that are not possible in the printout: with cross-references and literature references, you don't have to scroll to the target , you can jump directly to the target page by clicking on the link. Navigation within the document is also facilitated by page icons or the display of structure trees (according to the table of contents). If you click on external links, the target document is displayed in the web browser . However, these functions have to be "built in" by the authoring software (for example with LaTeX and the LaTeX extension package hyperref, see # TeX / DVI ) and implemented by the viewer .
- Courier (in the variants standard, bold, italic, bold-italic)
- Helvetica (in the variants standard, bold, italic, bold-italic)
- Times New Roman (in the variants standard, bold, italic, bold-italic)
- Zapf dingbats
PDF in operating systems
With the macOS operating system from Apple , PDF was used as the standard format for both screen and print output for the first time. The PDF generation can be done from any program that has a print dialog. Since PDF is also used to generate the print data, it is possible to output PostScript on non-Postscript printers. Almost any type of document that can be printed can be converted to PDF. This possibility is also available under GNU / Linux. B. in the print dialog of the desktop environment Gnome, the option of PDF generation is offered natively.
The free Adobe Reader / Acrobat Reader is available as a PDF viewer under Windows , Mac OS Classic and macOS, GNU / Linux and the Unix operating systems Solaris , HP / UX and AIX . The integrated Lucide viewer is available under eComStation . Since Windows 8 , Windows also has an integrated PDF viewer. Windows 10 was also equipped with a PDF printer by Microsoft.
For Unix-based systems, there is also the Xpdf program , which is reduced to the most basic functions (display on screen, searching the document, printing), as well as a few other programs ( Okular and Evince ) that are adapted to your desktop environment. These open source programs are also suitable for circumventing the supposed "security features" of PDF documents - it is sometimes possible to print out documents, although the author actually wanted to deny the viewer of the document this option.
Details of the side geometry
Information on the page geometry in a PDF document is particularly important in the printing industry . They describe in which area of a page the content is located that corresponds to the trimmed final format and where a further processing program (e.g. for imposition , i.e. mounting pages on a print sheet) can expect a trim allowance. Modern DTP programs store this information in PDF when exporting directly to PDF. If PDFs are output via PostScript, the corresponding information is usually not included. For PostScript output from certain programs, Adobe Acrobat Distiller is able to derive the net page area from the crop marks, provided these were also output.
MediaBox (media frame)
It defines the size of the output medium of the PDF document. The document has not yet been trimmed and usually contains the PostScript page size set in the PDF generator. The MediaBox must always be the largest of all boxes, as it must include all other boxes, and it is the only box that must always be included in a PDF.
CropBox (trim box)
The CropBox (sometimes referred to as the mask frame) describes the area of a PDF page that is to be output on the screen or on the printer. The values of the MediaBox are preset.
BleedBox (bleed frame)
A bleed box contains information about the bleed frame , which defines the size of the final format plus the intended trim (overfill). In the printing industry, a trim of 3 to 5 mm per side is usually required. An application example are images that are in the bleed (i.e. directly on the edge of the page) or images that slope down and are trimmed at the edge of the page. For an A4 page that is to be delivered to a printer, a bleed box of 3 mm results in a width of 210 mm + 6 mm and a length of 297 mm + 6 mm, i.e. 216 mm × 303 mm . The values of the CropBox are preset.
TrimBox (trim box)
The TrimBox is the final format of the document without any trim.
ArtBox (object frame)
The ArtBox (also called bounding box ) describes the page section that is to be used when placing the PDF page in another program; comparable to the size specification for importing an EPS file.
In addition to text and graphic elements, PDF documents can contain interactive form elements for form processes. Complete forms can thus be bundled in one PDF document; The data recorded in the document can be sent back to the publisher of the form in various ways.
- Print and fill in: The hand-filled form can be sent in conventional ways by post or fax.
- Completion and printing: The electronically completed document can be printed out and sent in conventional ways.
- Fill out and send via HTTP connection: The electronically completed form can be sent electronically via the web browser or from Adobe Acrobat.
- Fill in and send the electronically completed form by email.
Conversion of other formats to PDF
PDF documents can be created from XML data in two steps:
- Transformation with the help of an XSLT stylesheet into the XSL-FO format
- A PDF processor (for example Apache FOP , Altsoft Xml2PDF ) generates the finished PDF document from this.
PDF documents can be generated from an HTML file with the HTMLDOC program. This program has both a console interface and a graphical user interface. It is thus both on a client for direct operation by the user and for server use, e.g. B. suitable for on-the-fly generation of PDF documents.
The wkhtmltopdf program enables the generation of several PDF documents at the same time, possibly including a table of contents. Using the Webkit browser package, very high quality documents, e.g. B. for the documentation of complete websites. wkhtmltopdf is a console program and can also be operated via the Perl module WKHTMLTOPDF.
Also PDF.js converts PDF files (temporarily) into HTML code to display to enable this in the browser.
TeX / DVI
- From DVI files (the format was designed in 1979), which are created by the typesetting programs TeX and groff (among others), PDF files can be created in different ways:
- It generates from the
.dvifile using the device driver dvips a PostScript file (
.ps) and out of this with the Adobe Distiller or Ghostscript -Teilprogramm ps2pdf one
- Programs such as dvipdfm or dvipdfmx , which convert DVI “directly” into PDF, are a “partial abbreviation” of this method .
- It generates from the
- pdfTeX and LuaTeX are further developments of TeX , which "directly" generate PDF files without the intermediate format DVI. These extensions of TeX became important at the beginning of the 21st century.
For many TeX users, the alternatives to the first mentioned method are sufficient
dvi→ps→pdf. Other TeX users, however, embed PostScript in the source code to such an extent that these methods fail. This is especially true when the TeX package PSTricks is used. The additional packages pst-pdf, auto-pst-pdf and pdftricks make things easier in this case. Overall, however, there remain cases in which the “traditional” method is
dvi→ps→pdfirreplaceable. But there is another alternative
- XeTeX , which appeared after pdfTeX and a little earlier than LuaTeX. It creates an intermediate format XDV and from it (hardly noticed by the user) PDF with the driver xdvipdfmx. This is intended to fully process PostScript in the document source code. A package called xetex-pstricks is also available for the use of PStricks .
3D PDF documents are PDF documents that contain either a U3D surface model or a BREP / surface model PRC . They are mainly used to visualize CAD data, but are also increasingly used in scientific publications.
The free Adobe Reader from version 8.1 can display, animate, cut and measure both formats. With Acrobat 3D V7, 3D data from 40 CAD formats could be converted into 3D PDF files; however, in 2010 Adobe handed over the development, sales and support of the 3D PDF converter technology to Tech Soft 3D and PROSTEP AG. As of Acrobat X, the conversion is only available as a chargeable 3D PDF converter plug-in from Tetra 4D.
Some CAD programs such as Allplan or SolidWorks have a 3D PDF export; Allplan also offers a 3D PDF import. Tools such as Deep Exploration from SAP, Pages3D from QuadriSpace and 3DVIA Composer from Dassault Systèmes can also save 3D CAD models as 3D PDF.
In addition to the 3D data as visualization, other relevant information about a CAD model can also be inserted into a PDF. For example, the data of the finished model can be shown as a 3D visualization for the production of a sheet metal part.
From Acrobat 9, various video formats converted into Shockwave Flash (SWF) can be embedded in Adobe PDF. This means that videos, animations and applications can be used on many platforms. Due to the Adobe Flash support in Adobe Reader version 9 or higher, no additional player is required for playback. Since the last patch for Adobe Acrobat and Adobe Reader 9, Adobe has changed the default behavior for 3D PDF, including removing the Flashplayer from Adobe Acrobat 9 and Adobe Reader 9 - Flash content accesses the Flashplayer in the operating system. Adobe Acrobat X and Adobe Reader X are not affected as there are almost no attacks. 3D data, SWF functions, and SWF video formats can also be combined; this makes it possible to cover parts of the model with SWF videos and functions.
Office application files
Versions of PDF
|year||PDF version||Adobe version||Characteristics|
|1993||1.0 / PDF||1||Visually attractive text display, embedding of bookmarks and internal cross-references, reader is called Carousel|
|1994||1.1||2||external cross-references, embedding multimedia files in sound and video formats that are now obsolete, documents can be searched, 40-bit encryption|
|1996||1.2||3||Possibility of using the CMYK color model , direct opening in the browser window through implementation of browser extensions (so-called plug-ins), accessibility plug-in for the blind for Acrobat Reader 3, interactive elements such as checkboxes and radio buttons are possible|
|2001||1.4||5||Elimination of the accessibility plug-in, but support of MSAA (Microsoft Active Accessibility) by Acrobat Reader, RC4 encryption with 40–128 bits, description of the logical document structure with tags|
|2003||1.5||6th||Embedding of images in JPEG 2000 format , films in MPEG format and audio files in MP3 format possible, public key encryption PKCS # 7 ; Reading program is now called Adobe Reader, no longer support for DOS-based Windows versions (Windows 95, 98, ME)|
|2004||1.6||7th||Support for the universal 3D file format, embedding of OpenType fonts, support for XFA 2.2 rich text elements and attributes, AES encryption, PKCS # 7 encryption with SHA256 , DSA up to 4096 bits, inaccessible PDF documents with tags, better support for multi-column documents, form fields can be read out with the help of the speech output functions, PDF creator with accessibility assistant: supports the optimization for screen readers and screen magnification programs|
|2006||1.7||8th||further improvement of the 3D display options, stronger encryption algorithms (PKCS # 7 with SHA384, SHA512 and RIPEMD-160 , 256-bit AES)|
|2017||2.0||DC||Support for the PRC file format, 3D measurement tools, improved security functions|
Norms and standards
Since 1997, standards on the basis of PDF have been developed and adopted in various ISO committees . Minimum requirements and restrictions are defined based on specific PDF versions. In this context, Adobe Systems has assigned the relevant ISO committees the right to make the necessary specifications available for download for an unlimited period of time.
As a rough approximation, these standards correspond to the different versions of PDF as a basis:
|ISO||year||Type||version||Designation / remark|
|15930||2001||PDF / X||1.3||Format for the transmission of artwork|
|15930-1||2001||PDF / X-1a||1.3||see PDF / X|
|15930-5||2003||PDF / X-2||1.4||see PDF / X|
|15930-4||2003||PDF / X-1a||1.4||see PDF / X|
|15930-3||2002||PDF / X-3||1.3||see PDF / X|
|15930-6||2003||PDF / X-3||1.4||see PDF / X|
|15930-7||2008||PDF / X-4||1.6||see PDF / X|
|15930-8||2008||PDF / X-5||1.6||see PDF / X|
|19005-1||2005||PDF / A-1||1.4||Format for electronic archiving|
|19005-1||2007||PDF / A-1||1.4||Correction PDF / A-1|
|19005-2||2011||PDF / A-2||1.7||see PDF / A-1|
|19005-3||2012||PDF / A-3||1.7||see PDF / A-1|
|24517||2008||PDF / E||1.6||Format for technical documents from the fields of engineering, architecture and geographic information systems (PDF engineering)|
|-||2008||PDF / H||Healthcare Document Format (PDF Healthcare)|
|14289||2008||PDF / UA||1.7||Guidelines for creating an accessible document in PDF (Universal Accessibility) format|
|16612-2||2010||PDF / VT||1.6||Format for use in high-volume and transactional printing (PDF Variable and Transactional Printing)|
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