or the free foxit pdf reader at http://www.foxitsoftware.com/pdf/reader/reader-interstitial.html. Both work equally well.
If your browser and default pdf viewer has trouble opening these files within a browser window:You should save these files to your computer and then open them. If you are using Internet Explorer you should Right click on the file and select "save target as" then point to a convenient location you can find again like your desktop. If you are using Firefox, Right click on the file you want to save and select: "save link as" and save it to a convenient location. If you still have problems your might have corrupt pdf viewer program files and you should download it again and reinstall.