Microsoft Compiled HTML Help


Microsoft Compiled HTML Help is a Microsoft proprietary online help format, consisting of a collection of HTML pages, an index and other navigation tools. The files are compressed and deployed in a binary format with the extension.CHM, for Compiled HTML. The format is often used for software documentation.
It was introduced as the successor to Microsoft WinHelp with the release of Windows 98 and is still supported in Windows 10. Although the format was designed by Microsoft, it has been successfully reverse-engineered and is now supported in many document viewer applications.

History

Microsoft has announced that they do not intend to add any new features to HTML Help.

File format

Help is delivered as a binary file with the.chm extension. It contains a set of HTML files, a hyperlinked table of contents, and an index file. The file format has been reverse-engineered and documentation of it is freely available.
The file starts with bytes "ITSF", for "Info-Tech Storage Format".
CHM files support the following features:
The Microsoft Reader's.lit file format is a modification of the HTML Help CHM format. CHM files are sometimes used for e-books.
Sumatra PDF supports viewing CHM documents since version 1.9.
Various applications, such as HTML Help Workshop and 7-Zip can decompile CHM files. The hh.exe utility on Windows and the extract_chmLib utility on Linux can also decompile CHM files.
Microsoft's HTML Help Workshop and Compiler generate CHM files by instructions stored in a HTML Help project. The file name of such a project has the extension.HHP and the file is just a text with the INI file format.
The Free Pascal project has a compiler that can create CHM files in a multiplatform way.

Use in non-Windows applications

Read support:
Read/write support: