Reading pdf files, requires a pdf reader such as "Adobe Reader".

installation instructions (on Windows XP SP3)

(Note: Adobe Reader now includes "Adobe Air".)

Go to
  > Click  "Free! McAfee Security Scan" to de-select it.
  > [Download now].

Then follow the displayed instructions, E.g. if using Firefox...
  > [Save File],
  > Double click "install_reader10_uk_air_mssd_aih.exe".
  > [OK]
  > check "Publisher: Adobe Systems Incorporated"
  > [Run]
  > [FINISH].

Then on the first attempt to open a pdf, click
  > [Accept]