How did you "link" them? did you insert them into container fields using Insert File | Store a Reference? (That does not require a plug in, by the way. Did you mean, perhaps, that you updated the Adobe Reader application on your computer?)
It's possible that a version of Filemaker this old may not be compatible with the latest Adobe software. In which case, you'll need to either roll back your adobe software to the earlier version that worked or upgrade to a newer version of FileMaker.
Yes, I “linked” them by inserting an object created by file. And, yes, I recently updated the Adobe application on my computer. Thanks for your suggestions.