Thanks Graham,
The documents were originally created with word 2010 then I converted them to pdf to send to my lecturer for marking. The comments were added by my lecturers, but they wont open since I upgraded. Even comment balloons from earlier assignments that I could open before, wont open now that i've upgraded to office 2013. But I will try your suggestion and convert them back to word and see if I get anywhere with that. I think all my pdf documents open with adobe reader automatically.
Thanks again,
julzmacha.