chm

CHM stands for Microsoft Compiled HTML Help, a proprietary help file format used to package software documentation into a single, browsable file with the .chm extension. It was introduced by Microsoft in the late 1990s as part of the HTML Help system.

CHM files are binary containers that embed HTML documents, images, and other resources. They are produced from a collection of HTML files and metadata files using the HTML Help Workshop compiler, which processes a project file (.hhp) and associated contents (.hhc for table of contents and .hhk for index). The result is a self-contained help file that can be viewed offline.

Viewing is done with the HTML Help viewer, originally integrated as an ActiveX control (hhctrl.ocx) or a standalone viewer (hh.exe) on Windows. Features include a navigable table of contents, an index, full-text search, bookmarks, and hyperlinked navigation among the embedded HTML pages.

History and usage: CHM was widely used for software manuals from the late 1990s through the 2000s, particularly on Windows. As web-based documentation and modern help systems emerged, CHM usage declined; Microsoft stopped active development of HTML Help in favor of newer technologies, and some packaging and distribution contexts have moved away from CHM.

Compatibility and security: CHM files are best viewed on Windows with the official viewer or compatible third-party software. On other platforms, CHM viewing requires additional programs such as KChm, xCHM, or Calibre. Security considerations include the potential for embedded scripting to access local resources, so some environments restrict or warn about CHM content.