The Freedom of Information Act has proven to be an very useful tool for government transparency over the last four decades. Traditionally, this information has always been revealed on paper, with the sections deemed "sensitive" redacted from the document with permanent market.
However, today is a new day, and now most documents are kept in a fancy non-editable format like PDF anyway, so when the TSA recently decided to publish their Screening Management Standard Operating Procedure online (outside of a FOIA request, go government transparency), they decide to redact it by doing what was familiar: drawing over the sensitive data using black boxes.
Of course, in a OCR'd PDF, that doesn't actually block any data. You can still highlight and paste the data, since it's still in the text, even though you can't see it. Great job, TSA.
The original document's been pulled, but the good folks over at Cryptome have the document, with the black boxes replaced by red ones so you can still see all the data, which I'm perfectly okay with. This information really has no business being classified as sensitive, but that's my opinion, I guess.
So, when you're going to be redacting information from a document, especially one you're willingly offering. You might want to make sure you've actually kept the information you want to keep secret, secret.