To read a pdf document you only need a pdf reader, such as Adobe Reader or Foxit. You don't need either Word or OpenOffice.
If you've got Adobe Reader but can't open a pdf then one of the following must be true:
(a) the file that you've received is corrupt ; or
(b) Adobe Reader isn't working properly ; or (most likely)
(c) your computer has lost the 'file association' that tells it which program to open pdf documents with.
Try saving the file, rather than opening it directly. Then right-click on the icon for that file and select 'open with'. Do NOT simply click on 'Adobe Reader' but select 'Choose Program' instead. Then select 'Adobe Reader' and put a tick where it says 'Always use this program . . . ' before clicking 'Open'.
Chris