Pirform allows you to save certificates in a common format called Portable Document Format, or PDF for short. To be able to open PDF files you will need to install a program that can open PDF files. One such program is the free Foxit PDF Reader, which you can find from here:
Just download and install this program and you will then be able to open the PDF versions of your certificates that Pirform produces.
Note: When you install the program, it may ask you to install trial versions of other programs or browser toolbars. Generally you will want to say no to these offers.