As per my experience with Microsoft HTML Help, it doesn’t decompile compiled help files (.chm), but only compiles HTML files into CHM ones. BTW it can be found as a component in the VS installation, check Add/Remove components of VS. Its main disadvantage is that it isn’t user friendly! So I used to use 3rd party SW for this task, naming:
PS: All these programs use (call) HTML Help behind the scenes, some of them, if not all, require that HTML Help Workshop be installed in order to use them.
Take a look here:
Here is last version of Sandcastle (requires MS .NET Framework and HTML Help Workshop):
- How to easily benefit from Microsoft HTML Help Workshop
- Download HTML Help Workshop and Documentation