That's an Acrobat question. There should be prepress people in the Acrobat forum who should be able to answer that.
If you need to do this in Photoshop you can open the PDF there, convert, and resave as PDF. Post some screenshots so that we can see what the exact issue is.
Oops, I thought I was in the Photoshop forum, sorry about that...
Yes, this is the right place.
It sounds to me like you've lost the links to the images and what is converted are preview images. There should not be any compression in the convert process.