If you're trying to download the PDF file (to save on your disc), right-click on the PDF link and chose "save link as" -- this will save it instead of trying to open it inside Chrome.
If you want to open it inside of Chrome, instead of saving it into a disc file, go to this Chrome settings page: chrome://plugins and look for the built-in Chrome viewer for PDF files. Usually this is enabled by default, but if PDFs aren't displaying it may have been turned off. (Note that the "chrome://plugins" URL isn't a real URL, and doesn't have "http:" in front of it. It's just a way of opening Chrome's plugins configuration page.)
I hope this helps,
Allen