export as jpeg and create new pdf
I had a similar problem with a scanned book downloaded from internet. I was able to see it in MAC but in Ipad all pages appeared as white.
I tried using the "optimizing" feature of adobe PDF but it worked only partially, I was able to see some random pages in the ipad. Then I tried to use the preflight option of adobe which supposedly fixes pdf according to standards but then the displaying in the ipad was painfully slow, loading a page would take 10 seconds or more.
What I did finally was export every page to jpeg in good quality using adobe acrobat, and then create a new pdf mixing all the pages. This time it works and I can see it in the iPad all right.