[gaazoh]

I just had the exact same reaction! So I opened a random PDF I had laying around, and yes, it's mostly a text format. Some (most) objects are binary data streams, but some are also text data. Likewise, objects may or may not be compressed, obviously compressed streams are binary data. But the file structure is text, some objects are xml, and you can figure out quite a lot of stuff just by looking at a pdf in a text editor, and it might not even be that long: the single page PDF I just looked at is just over 1500 lines long, I can definitely manually scroll through it (although offsets are in bytes, not lines, which make them not very useful for manual lookup).