It's ok now. If you don't install the 32 bit version along the 64 bit version the help files won't install. I did a new install including the 32 bit version and can read the online help now with th documentation of the api.
Thanks for this information, as I also could not find the documentation. After you install the 32-bit version, both the libraries and all documentation is located at: C:\Program Files (x86)\SOUND FORGE Shared Plug-Ins
When both the 64 and 32 bit versions of SF Pro are installed, they share much of the settings and data files. So if one is uninstalled, it 'could' remove some of the shared files as well. The third-party 'Revo Uninstaller' has options to choose what is removed.
The issue is if you only install Sound Forge 64-bit, the development libraries and documentation will never be installed at all. I run 64-bit Windows and did not install 32-bit SF. Most people also would not install it either. The issue is the components will never be installed if you do this. The the 64-bit and 32-bit development libraries get installed under Program Files (x86). You do not want to removed the SHARED FILES. These are the files we were looking for in the first place.
Well, If you install the complete package everything is fine and in place. You can then uninstall the 32 bit parts via the Windows 10 Start -> Settings -> Apps without losing the help files. Everything stays in place. Obviously the bug is only in the installer if you install the 64 bit version exclusively. BTW: Surely I reported it to the support.