When I was involved with a contract negotiation, they emailed me a pdf offer with addresses, names and important numbers retracted with black and asked if these terms are OK with me and we can talk about the numbers.
I noticed that when I select a region of text with a mouse, the retracted' black text becomes white text over black background. It revealed name of our competitor, addressees and numbers in their offer, the whole retraction was just a typographic trick.
I think you meant "redacted" vs "retracted". But yeah, there are a lot of stories out there of people assuming a black bar over black text is high security.
There was a document released by the State Dept at one point where the redactions were just black box over the text. You could just select, copy and paste to see it.
I compared documents and maybe not surprisingly, they seemed relatively minor points.
I noticed that when I select a region of text with a mouse, the retracted' black text becomes white text over black background. It revealed name of our competitor, addressees and numbers in their offer, the whole retraction was just a typographic trick.
When in doubt, print -> scan -> convert to pdf.