Sad story. Pdf is kind of proprietary and, second, intended
for printing. People use it and, even more, like it. I have a lot
of documentation in that format and know how do you feel.
Something converts just fine in calibre, something not. With
pictures you are on the strange land and have a good chance
to be mad about that all. If you have the same docs in chm,
it converts perfect. How other manufacturer handle this issue?