What I really don't understand is Acrobat Reader. It has a "Protected View", which is the first WTF - .pdf-s are read-only, so there should be absolutely zero active code running anyways. What's the next, much bigger WTF WTF WTF is that you need to exit protected view to print the document.
How can the program read and render the document on screen, but not print it?! How is this even possible?
PDF can contain executable code (JavaScript to be exact), access remote URLs, and has several separate modes of display (which means that document rendered for printing is different than what you see on the screen).
PDF is an old complex format with a lot of features used in a lot of special cases that go light years beyond looking at a simple text file. It's the reason for all the issues, but keeping it useful as it is and magically waving away all issues is not really easy.
PDF is a very fancy wrapper around post-script (massive over-simplification). Post script is a Turing complete language. As such, PDF is essentially code.
What I really don't understand is Acrobat Reader. It has a "Protected View", which is the first WTF - .pdf-s are read-only, so there should be absolutely zero active code running anyways. What's the next, much bigger WTF WTF WTF is that you need to exit protected view to print the document.
How can the program read and render the document on screen, but not print it?! How is this even possible?