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iBooks will open it but will take a long time. If you want to use iBooks, open it and leave your iPad somewhere no one will disturb it. Give it about 10 minutes.
Some other alternatives are GoodReader, PDF Expert, ReaddleDocs, PDF Reader Pro.
 
IBooks does fine with the 700MB image PDF I have of the Calvin and Hobbes strips.
 
Ugh, mine does that too. I have a couple scanned textbooks in there that are large files. One of them opens fine, the other one...not so much. The one that won't open also refuses to be OCR'd by Acrobat (causes the app to crash every time), so who knows...
 
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