Corel Draw, maybe, if they were vector images. WordPerfect if they were using a word processing program.
(ETA: I still miss WordPerfect's Reveal Codes window. I love FM for many reasons, but I wish it were possible to do something similar. And yes, I know, "Use structured FM with an EDD and you'll have a close equivalent", but it's not the same.)
Ok, all. Problem solved after five days. Cannot believe how two simple PDF files would cause dozens of PDF images to not load. The problem was never the server, server path character size, book file size, Acrobat converion, or PDF insertions, etc. Placing the files on a hard drive didn;t solve the problem, either.
This was ridiculously simple but took five days to troubleshoot. There were two PDF forms in one section of the book that were fillable, and I didn't know it. Previously, they were not fillable forms and our company store changed them from flattened to fillable, electronic forms. Once I converted both to Word and exported to print-ready PDF (flattened), the problem was solved. This is probably one for our record books.