The 20-second redaction test: before you send a PDF
A black box drawn over a number in a PDF hides it from your eyes, not from the file. Syncfusion's guide on DEV (23 Jul 2026) puts it plainly: "Covering sensitive information with black rectangles doesn't actually remove it from a PDF." Copy-paste, search and AI tools read the text underneath. It has happened in court: in 2019, in the Paul Manafort case, journalists copy-pasted the "redacted" text out of a filing.
This test tells you in about 20 seconds whether the words are really gone.
What you need
The PDF you're about to send or upload to AI
A PDF reader with search (Command-F or Ctrl-F)
The test
Open the PDF and search for the hidden word or number. Type part of it, like the first few digits.
Select the text across the black box, copy it and paste it into a plain note.
Found it, or did it paste? It isn't redacted. Nothing was removed.
That's the check Syncfusion recommends: "Validate the redacted document by verifying that the removed content can no longer be found through search, copy-and-paste, text extraction, or PDF inspection tools."
Redact it for real
Use a tool that removes the text, then run the test again on the new file:
Acrobat's Redact tool.
The Adobe plugin in Claude, which can "redact sensitive information" in PDFs (Adobe, 24 Sep 2026).
On a Mac, Preview's Redaction tool. Apple's guide: "Select text to remove it from view. You can change the redaction as you edit, but once you close the document, the redaction becomes permanent."
Asked the same question about the properly redacted copy in the video, ChatGPT said: "The actual number is not recoverable from this file."
Some editors call a shape or a black highlight "redaction" and leave the words in. Whatever tool you use, the test decides.
The mistake to avoid
Drawing a black rectangle, or highlighting in black, and sending the file. The page looks redacted. The words are still in the file.