Thanks Peter! It looks at though the 2017 version would be compatible with my OS.
I found this thread: https://forums.adobe.com/thread/2314822
... and clicked the link to download RoboHelp 2017 but was instead prompted to download the 2019 version.
Do you know if it's still possible to download the 2017 version?
I couldn't find the classic version and I spoke with an Adobe Customer Service rep who told me that the 2017 version wouldn't be compatible with my PC. So I think I'll just wait until I have a newer PC with a 64-bit CPU and more RAM. In the meantime, Robohelp 2015 works just fine and the application does what I need it to do.
The 2019 version downloaded but wasn't usable.