In so many words: We can't know. You have not provided any details about your exact settings, what version of Acrobat, your placed images, color settings, color profiles and a million other things including perhaps providing your test fioles for inspection by other people. That aside simply ask in teh relevant ID/ AI/ Acro/ PDF forums. This place here is a dead place and only meant for general sales, install and activation questions, not specific workflow questions.
Mylenium