Here is a way to check which format it is in. Open the document in acrobat, go File / document properties / Summary. On that window it should give you the PDF version. if it is 1.2 it is compatable with Acrobat all the way back to Acrobat version 3. Which means it is something else causing the prob. Changing it if you need to means going through acrobat distiller and probably resaving / recreating it.
JD