Microsoft Compiled HTML Help replaces WinHelp
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 95 OSR 2.5 and consequently, Windows 98. Within the Windows NT family, the CHM file support is introduced in Windows NT 4.0 and is still supported in Windows 11. 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.