Another avenue worth exploring is to download another pdf reader program and see whether you can load the file and save it somewhere else with that.
Some pdf files just don't want to work with certain software and hardware combinations. I have a particular pdf file that refuses to load properly on an iPad using my usual viewer program, yet it works just fine with another app that allows pdf files to be viewed. It works fine on a PC with all viewers.
The error occurs at the same place in the file regardless of whether the file is copied to another application and edited and recoded, or not. Copying the file back and forth to a PC from the iPad makes no difference and downloading the file on a PC and then transferring it to the iPad results in the same error.
The closest idea I have for the reason this may happen is that the pdf compression algorithm results in a string of characters that the viewer program or the computer interprets as an end of file marker. Just a theory, but short of going through the pdf file byte by byte, it is the best guess I can make.
The only other idea is that with a particularly complex or large graphic included in the file, the iPad simply runs out of memory to decode that page. The page does contain some very detailed images and text.