Earlier quoted context omitted.
> and if it is a PDF, convert to an image afterwards because too many PDF editors use non-destructive operations to add a new object instead of changing what's underneath. You'd be surprised at how many times this happens on Government documents with redaction. :S
A friend of mine once had to review some (Swedish) court document with redacted witness names. It was a word document with history intact. Just undoing a few steps was all it took.
Document history was turned on and anyone who hit ctrl+z got the full class marks.
(The same lecturer initially failed me because they forgot to add my final exam score to my assignments score, and then took four months to fix it. They weren't very competent.)