To add or remove HTML topic files from a project file
Open a project (.hhp) file, and then click Add/Remove Topic Files.
Adds or removes HTML files from the project file. In the Topic files box, click Add or Remove.
Note
When using HTML Help Workshop, the number of topic files you can view and add is limited to 5,000. Projects with more than 5,000 files will compile correctly, and links from entries in the index and contents files will work, but you will need to use a text editor to view, add, or edit them.