So sorry, Rick, I had just written to someone else and hadn’t cleared his name out of my mental “cache”!
I am actually creating three separate links (in the pcs.chm), each to a file named index.html, in a three different subfolders stored in the Help directory (pictured below). So, I am trying to use relative links to the individual folders (hardware troubleshooting, ibasicLanguage, and system functions). Can I pasted the relative link directly in the “Program to open” line?
I hope I made sense.

Yes, the link might look like this: system functions/index.htm
While that *SHOULD* work, there are a couple of possible "gotchas".
1. The space in the folder name might cause a linking problem. If you have any influence over the naming, you might consider eliminating the space just to be on the safe side.
2. Depending on how the CHM is launched, the actual path may change a bit. For some reason when an application opens a CHM file the path gets wonky. That's where you need JavaScript code to deduce the actual path. 
Cheers... Rick 