A government report goes out with sensitive names hidden behind black rectangles. A journalist opens the PDF in Acrobat, selects the page text, and copies the redacted names directly out. This has happened repeatedly — at the DoJ, the FBI, the UK Cabinet Office, and several large law firms. The fix has existed for two decades. People still get it wrong.
Why the rectangle alone fails
A black rectangle drawn on top of text in a PDF is a visual element layered above the text — not a replacement for it. The text underneath remains in the document stream, fully extractable.
Tools that 'redact' by drawing rectangles produce a file that *looks* redacted but isn't. Anyone with a PDF reader can select the hidden text, copy it, paste it, and read what was supposedly hidden.
Where it goes catastrophically wrong
Manafort case 2019: Mueller report draft redactions were reversible — the redacted names were extractable from the document.
NSA dossier 2020: Snowden-era documents redacted via Acrobat Comments tool leaked underlying content.
Pentagon Afghanistan documents 2021: redacted passages were copy-paste-able.
Each case made international news. Each was avoidable with proper redaction tooling.
How to do it right
Use a tool that removes the underlying content — replaces the text bytes with the redaction marker bytes — rather than just drawing over the top. Flint's redaction tool does this. Adobe Acrobat's redact tool (not the highlight tool, not the rectangle tool) does this. Some open-source tools (Master PDF, qpdf with care) do this.
After redacting, verify: open the output, select-all in the redacted region, paste into a text editor. If anything appears, redaction failed.
Belt and braces
For very sensitive material, flatten the file after redaction — render it as images and re-OCR a clean text layer if you need searchability. Strip metadata. Re-check the file size — if it's the same as the original, that's a warning sign the underlying content wasn't removed.
For batch redaction (court bundles, FOIA releases), audit a sample manually. Automated redaction can miss edge cases that humans would catch.
FAQ
Is the Acrobat Comments tool sufficient for redaction?
No. The Comments tool draws annotations — including black rectangles — without removing underlying content. Use Acrobat's dedicated Redact tool, or Flint's redaction tool.
What about Preview on macOS?
Preview's redaction tools have improved but historically have produced overlay-only redactions. Test before relying on it.
Can I use a text editor to remove redacted content?
PDFs are binary files — text editors can't reliably edit them. Use a proper PDF redaction tool.
Does converting to image and back work?
It removes text-layer content but produces large files, breaks search, and loses accessibility. Better to use proper redaction tooling that targets just the sensitive parts.
Don't be the next redaction news story. Use a tool that actually removes the content.