You may already have a copy of the free Acrobat Reader program installed on your computer. For most users, if you click on a web page link to a PDF document (identifiable because they end in ".pdf") the file will open for viewing in your web browser. From there you can choose to print or save the file to your hard drive.
If you do not have Acrobat Reader on your computer, or have a version which needs to be updated (you'll be warned about the need to update when you open a file created with a newer version) you can download it and install it on your computer for free.
The Adobe Acrobat Reader can be downloaded from the Adobe Web Site. Find the file you need for your computer's operating system and follow the instructions on that web page if you are unsure about the installation routine.
Other readers capable of view PDF files also are available, including the Foxit Reader.