One of the annoying things we’re seeing more and more of these days are sites allowing the copying of PDFs from the original publisher and placing them on their server as part of some sort of “library”. All they are trying to do is benefit from search engine traffic to their site for somebody else’s content, for various purposes.
It’s one thing to provide a link to a PDF on the publisher’s web site, it’s completely another to post it on your own server without permission.
If it doesn’t look like the correct site to view a specific PDF as the link from Google, Bing, etc.,… it probably isn’t. Find the right site and go there. Save yourself the question of its legitimacy and currency, and don’t provide improper users any benefit.