I've been working on a CAD file with PDF underlays attached. Haven't had any issues with them. Today I opened the file and the PDFs won't show. The PDF is still in the same location. The outlines of the PDF show, but the content doesn't. I've tried unloading, reloading, refreshing, etc. Nothing shows them. I don't want to lose all the work I did to place them. Any ideas on things to try?