RECAP: bluegiraffe24, the hypertext markers you were using are great for opening files from within FrameMaker, but not usable for HTML5. In fact, I'm surprised they survived the PDF process.
A cross-reference is a faster, more accurate, updatable method of entering the text and the needed link. You'll want to replace all of your "open file" hypertext markers with cross-references, and you can use the Find/Change dialog to quickly find each instance of the "open file" markers and then insert the more appropriate cross-reference.
**I love that we'd run into each other at this year's STC Summit in FL...great catching up with you again!