A black rectangle drawn over a Social Security number looks redacted. It usually isn't. A surprising number of leaked "redacted" documents — including some embarrassing ones from government agencies and law firms — have had the hidden text recovered in seconds, just by selecting and copying it.
What actually happens when you draw a box
Most PDF editors and annotation tools add the black box as a separate object layered on top of the page — it's a shape sitting above the text, not a replacement for it. The underlying text is untouched: still present in the PDF's content stream, still selectable, still extractable by anyone who copies the text, removes the annotation layer, or runs the file through a basic text-extraction tool. Visually covered is not the same as gone.
What real redaction requires
Genuine redaction has to remove the underlying content, not obscure it. That means rasterizing the marked region — converting that part of the page into a flat image with the sensitive text baked out of existence — rather than layering a shape over live text. Once a region is rasterized, there's no text object left to select, copy, or extract; the pixels underneath the black box simply don't contain the original characters anymore.
A simple test before you send anything
Before sharing a document you believe is redacted, try selecting text over and around the black boxes, or paste the page into a plain text editor. If anything sensitive shows up, or if you can select through the box at all, it wasn't actually redacted — it was just covered.
Redact PDF does this correctly, in your browser
DocZap's Redact PDF tool rasterizes the regions you mark rather than layering a shape over them, so the underlying text is genuinely destroyed — and the whole process runs locally, so the sensitive document never has to leave your device to be redacted.
Try these DocZap tools