What version of Acrobat was the original pdf file created with? Does it open and display properly in a later version of PS? I had the exact same problem when trying to open a pdf file from a webpage using (I think) Acrobat Reader v. 3. It was all just little squares. I updated to Acrobat Reader v. 7, and then it displayed perfectly.
You may want to try saving the pdf file using an older version of Acrobat or Adobe Reader, if that’s possible. If not, see if you can open it in a regular word processing program and then save again. Or see if a more current version of PS will open the pdf as is.