While making some updates to the site, I attempted to change a .pdf link on a resources page of my site. However, the link box listed the document that the link pointed to as '80.' Every single document link pointed to '80,' and every time since I've tried to change it, VSD changes it back to 80. I've tried several different file types in various locations on the computer, but nothing works.

Any idea what the problem could be? I'd greatly appreciate any help.

That should be fixed in the later version(s) of VSD (5.9.4 for sure).
Download & update to the latest.