Ok, that is correct as far as it goes. That's what PDF files all look like at the start. But, it seems something has damaged other parts of the file. That seems certain, since multiple software from different companies is failing. Something to do with the Mountain Lion upgrade? I hope not, but it is something in common. Here's something to check out. Pick one of these files you know well, and which you downloaded a long time ago. Now, check the modification date in Finder. Is it recent? Ok, check another, is it the same sort of time? If so, probably something/someone wrote to those files at that time. Can you remember what was happening then (e.g. was it when Mountain Lion was installed, or something else?) Meanwhile, the chances of being able to recover the files is slim. Time to look at your backups.
... View more