Open Ubuntu Software Center and search for PDF reader. There are quite a number of them you can try them one at a time and see if any of them can read the file. If not you can uninstall them using Ubuntu Software Center.
You can download Adobe Reader from Their official website. The page will take you to a FTP site and you have to drill down the directory structure to find the latest .deb file. As of this writing it was
Download the file and double click on it to open it in Ubuntu Software Center. Click on the Install button and follow instructions if needed.
Best of luck.