HTML Help files are built from multiple source files:
Content files, especially standard HTML files, communicate core information to the user, either through static text and graphics or through advanced web-page-style behaviors and scripts normally available in web pages.
The Help Contents file uses .hhc for its file extension. Using standard HTML
<li> tags, the file specifies the hierarchical table of contents used by the help file.
The Help Keywords file uses an .hhk file extension, and documents the index used to access help pages from specific predefined keywords.
The Help Project file, using an .hhp file extension, defines an entire help project and its target .chm file. This INI-style text file identifies all the other files that will be compiled into the target help file. It also defines a few project-wide options.
You can build the primary content files by hand using any standard HTML tool you wish, as long as the output format matches what is expected by the HTML Help Compiler (supplied by Microsoft). For the content files, it generally doesn't matter what tool you use since standard HTML is sufficient. Any hyperlinks that you include in the content to other help pages in the same directory will become standard help links in the compiled help file.
The non-content files require a very precise format; they are all based on HTML, except the Help Project file, which is an INI file. You will need to either design these files by hand using the expected ...