I'm currently in OneNote 2016. Randomly, files that I have attached to pages in onenote will fail to open, particularly PDFs.
It never happens right away: anything I attach is then openable immediately. But when I return to files a week, a year, or a decade later (yes, I've been using OneNote for a long time), occasionally files will fail to open. There doesn't seem to be any pattern as to when or which ones will fail. For very similar PDFs embedded on the same page, one won't open and the other will.
It seems like OneNote has actually corrupted the files because even if you right click and "save as" to desktop, the files still fail to open. These are all files that originally were 100% fine, and I'm sure of it, but somehow over time they start to fail when stored within OneNote.