[popoff]

You must think that this kind of classical books aren't just compilations, they are complete jobs from an author and the rigth way is to maintain the pdf in the original format (for further sharing or printing).

If companion store the last pdf file as a cache and only change this cache when the "create song" function is called and not when "copy song", the job is done. I think that it's very simple put this behaviour in the code.