PDF is pretty much a symbolic representation of what needs to be printed out. It's symbolic so it can get rasterized onto whatever device in question, in a way

PDF is pretty much a symbolic representation of what needs to be printed out. It's symbolic so it can get rasterized onto whatever device in question, in a way that should be as accurate as possible to a print version. That's the primary requirement of PDF, and has been since the beginning. They added a bunch of interactive stuff to it, which are used occasionally (forms). But to understand PDF you need to understand the above first.