Yeah I was a little surprised that this didn't go beyond the simplest xref table and get into streams and compression. Things don't seem that bad until you realize the object you want is inside a stream that's using a weird riff on PNG compression and its offset is in an xref stream that's flate compressed that's a later addition to the document so you need to start with a plain one at the end of the file and then consider which versions of which objects are where. Then there's that you can find documentation on 1.7 pretty easily, but up until 2 years ago, 2.0 doc was pay-walled.