An HHP file is a help project created by HTML Help Workshop, a program that helps users create help systems to distribute with software or a website. It contains help project information used to compile into a .CHM file. HHP files are created when a user saves a project in HTML Help Workshop.

When you are done editing and adding the information in your project you can compile it to the CHM file. The information stored in the HHP file is used by HTML Help Workshop to combine the help topic, related images, index information, and other help contents into the CHM file. You can then test the CHM file and customize it to match the appearance of the rest of your help system.