If you DO have Adobe Acrobat Reader installed, try downloading the file first (most of the time, right-clicking the link to the file and choosing to save it will work for that). Once the file is downloaded, you should be able to open it using Reader. Some web browsers have their own pdf viewers and try to use them to open the pdf inside the browser. Some browser pdf viewers can't open certain types of pdf files so, you get the message you got.
... View more