To read pdf files you will need to have the correct software. PDF (Portable Document Format) files require the Adobe Acrobat Reader (or similar) which is available free from Adobe. It can act as a plugin with your Internet browser so that PDF files are automatically opened in the browser.
If you have problems reading or downloading large PDF files, you might want to try converting the the PDF into a HTML file which you can then read in your internet browser. This video explains how to convert a PDF into HTML.