If you already have HTML Help Workshop installed and GhostDoc can't find it, you may have changed the default location. GhostDoc is looking for ProgramFiles(x86)\HTML Help Workshop\hhc.exe or ProgramFiles\HTML Help Workshop\hhc.exe
You need Microsoft HTML Help Workshop (compiler for .CHM files) when you want GhostDoc to generate help documentation in a compiled help (.CHM) format.
The Microsoft HTML Help compiler is available for download from Microsoft free of charge.
Microsoft HTML Help Workshop Download
After installing HTML Help Workshop, you may see a message that you "already have a newer version of HTML Help." Please ignore it! This message refers to the run-time components for displaying HTML Help on Windows, and on current computers, the existing runtimes are always newer than those in the HTML Help Workshop package.