PDF was not designed to be editable, nor for anyone to "work with" it in that way.
It was designed (at least the original purpose circa 1989) to represent printed pages electronically in a format that would view and print identically everywhere. In fact, the initial advertising for the "value" of the PDF format was exactly this, no matter where a recipient viewed your PDF output, it would look, and print, identically to everywhere else.
It was originally meant to be "electronic paper".
