Be sure it's not downloading as a text file instead of a PDF. There is a bug for some people that even when downloading the PDF, it opens as a text file and not a PDF or has gibberish when viewed with Adobe Reader. If you click to download the PDF, but it's showing up as a text file, change the file extension of the downloaded file to PDF, and see if that solves it. If not, then try viewing the PDF with a different browser, or downloading it first, then try opening it with Adobe Reader.
