You must have a reader software to open a PDF file.
Adobe Reader is widely used and free application that you can use to read PDF files. It can open standard PDF files and PDF portfolio with multimedia. It is the most powerfule PDF reader but slower and larger than the others. Adobe Reader has both the Windows version and the Mac version.
Foxit Reader is a faster and lighter application that can view PDF files. It is easy-to-use, the latest Foxit Reader has commenting tools, you can highlight, underline, add comments or some other basic editing functions. It is available for all windows based operation systems.
Preview is a built-in application that makes it easy to read PDF and popular image files on Mac OS. It has the basic editing capabilities such as resizing, rotating, annotating etc. It is the best PDF reader for Mac OS.
Lighten PDF Converter apps also have the built-in PDF reader, you can eaisliy read a batch of PDF files.