CHM (file format)

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Compiled Help Modules
File extension : .chm
Developed by: Microsoft
Initial release: 1997
Type: Help file
Expanded to: .lit

CHM ( Compiled HTML Help , also Compressed HTML Help or Compiled Help Module (s) ) is a file format from Microsoft that is used for help files under the Windows operating system . The associated system for creating and displaying the files is called HTML Help .

CHM files are compressed archives that in turn contain various files such as help texts in HTML format, images or JavaScript in compiled or packed form.

The format is a Microsoft ITS file format (InfoTech Storage) (similar to an LZX archive). In addition to the help files, metadata are also stored in the archives , which describe the structure of the displayed documents and which are evaluated by a corresponding display program. The structure of this metadata is documented on various websites.

Many e-books are available in CHM format.


The format was introduced with Windows 98 and replaces the RTF -based WinHelp format. It served as the basis for the .lit file format, a file format for electronic books that was abandoned in favor of the HTML-based Open eBook (predecessor of EPUB ).


CHM files are created using the free Microsoft HTML Help Workshop. Under Microsoft Windows, CHM files can also be displayed with the Sumatra PDF viewer (version 1.9 or higher). For the display of CHM files under Linux and other non-Microsoft operating systems there are e.g. B. chmsee , xchm , chmviewer and libCHM, the z. B. can be used comfortably with an eyepiece . The wxWidgets developer library contains support for reading CHM archives. A conversion to Portable Document Format is possible with chm2pdf .

See also

Web links

Individual evidence