The portable document format (PDF) was a file format developed by Adobe in 1993. The purpose of the file is to make document transfer much easier. In 2008, PDF became an open-source format. Previously, it had been proprietary. Many web browsers can read PDFs without having to save the file to your computer. However, should you save it to your computer, opening the file is easy. 

For the most part, if you double click on a PDF file, it should open right away in whatever program you have installed that can read PDF files. However, if this doesn't work, you'll have to do a few more steps. To begin with, right click on the file. This will open up a box where you have a bunch of different options such as copy, send to, etc. 

The one you want to select is the "Open With." This feature gives you a list of programs on the computer that can potentially handle that file. However, should you not have something, it'll say so and you can search on the web for a program that can handle that file format. One of the programs you're looking to have is Adobe Reader. How to Open a PDF FIle

Once you have installed the program–which is free if you choose Abobe Reader–it will now appear in the Open With tab. Click that feature and then drag over to the "Open With Adobe Reader." When you click this, the file will automatically open in the Abobe Reader program. Once it loads, you can then view the PDF.