PDF documents have the interesting feature that edits can be applied
just to the end of the file without altering the original content.
This makes it possible to recover previous versions of a document.
This is only possible if the editor writes out an unoptimized
version of the PDF.
This program removes the last layer of edits from the PDF document. If
there is just one revision, we emit a message and abort.
The --count option just prints the number of generations the document
has endured and applies no changes.