There's a story from years ago (I couldn't find it) about some government or legal documents having info redacted, but whoever did it just used some pdf editing tool to draw black boxes over the redacted parts, so all the info was still in the pdfs.
Edit: I found this but I'm not sure it's the one I'm remembering: https://www.techdirt.com/2014/01/28/new-york-times-suffers-r...