Or if the document is just text, simply scan it in black and white (as in, binary, not grayscale).

Perhaps an imagemagick pipeline dumping each page out as a png then blanking areas associated with a list of words (a pixel level concordance of the coordinates of all the words having been compiled from a text dump? Hand-waving here).

I'm probably overthinking this one but the various lengths of the redaction bars would provide some information perhaps? So three conspirators with names like Stonk, Hephalump and Pragma-Sasquatch would be sort of easy to distinguish between if the public had a limited list of people who might be involved?