HHP files are HTML Help Project files and store information on options, window types, merge info, a file list, text popups, information types, context-sensitive help, and subsets and are in INI format. Parts of the HHP format can be excised into text files and included from the HHP.
HHC files are HH Table of Contents files, store the Contents and are in Sitemap format.
HHK files are HH Index files, store the Index and are in Sitemap format.
STP files are HH Stop-list files, store the words to be ignored when generating search data and are in text format.
ALI files are HH alias files, store context-sensitivity links and are in text format.