I think you are completely out of luck here.
- I believe you created the project using Help Compiler Workshop. That would create a winhelp file from RTF files created in Word. Actually the way I created my first help file over twenty years ago. I would be amazed if anyone else is still doing that for the simple reason they will not run on later versions of Windows. I see there are some hacks but I have never seen anyone ask about them or report on them in this forum.
- Classic versions of RoboHelp allow you to import WinHelp to create a new project. I tried a number of options but everyone resulted in RoboHelp crashing. To be precise it closed without importing and did not create a new project.
- I then thought about RoboHelp for Word and seeing if importing the RTF files would provide a solution. RoboHelp for Word last shipped with RoboHelp 10, five versions back. Even if I had a copy it would not help as XP is the last version of Windows that was supported on.
- There is a program called FAR. It stands for Find and Replace but is a collection of many utilities and I believe but am not sure that it can create a CHM file from what you have. It used to be a paid for product but it is now free. www.HelpwareGroup.com
- With a CHM you could reverse engineer that into a RoboHelp project as described at Reverse Engineering (grainge.org). That would create a RoboHelp Classic project that you could then upgrade in RoboHelp 2020.
That's about all I can offer. Is there anyone supporting this forum who is familiar with using FAR or the Help Compiler Workshop who can add more?
ATM = At the moment?
The thread you pointed to suggests you may also be able to create a CHM using the Help Compiler Workshop. If that is what you are using that could be worth a try. If that works then reverse engineer that.
Finally given how long it is since WinHelp worked, how have you managed to keep this going?
Sorry it's not better news. Basically you have left the car in the garage and neglected it for too long, no surprise it won't start.