File type CHM, which means Microsoft Compiled HTML Help, is developed by American company named Microsoft for browsing and viewing Help. It is based on HTML, but it´s created from group of HTML pages, indexing file, which is opening file of document and some navigation tools. They serve for orientation in this file format (page moving, print, homepage, etc.). It is also used for showing software documentation.
First version was released in 1997 before the release of worldwide known Windows 98. In these times, he was meant to replace so called WinHelp, it was file format based on RTF format. Newer versions were added almost every year since the release of CHM file type. He was originally released together with IE 4, later on with Windows 98 and two years later was released with Windows 2000. One version was developed for IE 5.5 and Windows ME and the latest version was distributed in 2001 together with Windows XP and IE 6, which was component of this operating system. In 2003 the development was stopped, but its use is still continuing, because he´s supported in Windows 7.
Utilization of this file format is very big, because almost the vast majority of users are using Windows XP and Windows 7. Opening and editing can be achieved in 7zip, which can extract these files and allows you to edit simple pages. Out of Windows, this file type is readable in almost every operating system. For example: readers for Android are supporting him (King Reader), there´s also few utilities for Mac OS X – iChm or ChmPlus.