A couple of weeks back, the local authority around here sent out and published on their web site a consultation in PDF.  Now it worked up to the first link to another part of the file, but every link seemed like the H of http was HH, an hence none worked or came up with some strange errors. Like you, looking at the file it is apparently OK and if you use the mouse to click it is OK. They have now re encoded the files and uploaded them again, and sent me a word copy. and all is relatively well, except for text in and around maps. They know nothing about computers, but did tell me it was made using Google docs. That is something I've never used so I cannot comment. Had I known this topic was going to come up, I'd have kept a copy.
It does seem we get more than our fair share of errant PDF files. In this case it had been done originally in Word off site and encoded  in house to PDF.

It would be interesting to find out whether its some kind of masking out of extra data that is not normally seen, as it seems odd that merely clicking with a mouse will in effect not see the garbage.
Brian