Every now and again I link to a PDF file, and for those living in caves, you may think, "What?"
Anyhow, if ever you click on a PDF link and you cannot open or read the PDF file, most likely all you have to do is download a free PDF reader and you will be set to go!
You can download Foxit PDF Reader, which is my Windows default. It is small, fast and works really well.
You may also download the Adobe Reader which is available for Windows and Mac. It is bigger and loads a bit slower than Foxit, but is still good. However, PDF files should work fine on Mac since Mac's Preview reads PDF files fine.