Microsoft Compiled HTML Help (CHM) is a Microsoft proprietary online help format, consisting of a collection of HTML pages, an index and other navigation tools.
Although the format was designed by Microsoft, it has been successfully reverse-engineered and is now supported by many document viewers.
CHM was introduced as the successor to Microsoft WinHelp with the release of Windows 95 OSR 2.5.
[12] Lazarus and Free Pascal provide a doxygen-like tool for CHM generation and a separate command-line compiler called chmcmd.
The official viewer in Microsoft Windows (hh.exe) can decompile a CHM file.