Amusingly enough, people have even screwed this up. I recall some government agency trying to censor data with a black bar, but the problem was that the data was in a SVG-like document, so people could just delete the bars from the document and see the apparently-censored text.

I built a redaction process for a small company once.

My critical security step was rendering out the PDF as individual flat image files, then re-assembling it like a traditionally photo-copied document.

That way the loss-full operation is enforced, at the cost of forcing end users to OCR unsearchable image-scan (like) PDFs.

It's the only way to be sure!

You could replace the censored text with gibberish before blacking it out. Or some secret message for QAnons to find.

well if you had an open (.odf) or openable (.doc≈xml) format you could replace strings and be sure something was gone

It would be funny to place fake data behind the removable bars for tech savvy people to find.

> It would be funny to place fake data behind the removable bars for tech savvy people to find.

Tech savvy people, but also journalists

https://arstechnica.com/tech-policy/2021/10/missouri-gov-cal...

I remember a version of this happening with PDFs

Yep - Apple wound up adding a “Redact” tool to Preview.app for PDFs, likely in response to all the people who just drew shapes over selectable sensitive text.

https://eclecticlight.co/2020/12/11/how-effective-and-safe-i...

The EU has redacted PDFs this way a number of times, but I don't think anything truly sensitive ever leaked.

This has happened with PDFs many, many times.

I believe the US government did this at least once, by implementing the black bars in a PDF as a separate object, so the unredacted item was intact in the files they shared.

Whoops.

I remember that. Unredacted versions were also circulated.

> just delete the bars

I think you mean "illegally hack the black bars".

> I just go solid opaque bar. Way easier to do and harder to screw up.

There may be graphic design reasons you don't want to do that. A big black redaction bar isn't much of an illustration.