Check Whether a PDF’s Black Boxes Hide Real Text
Test whether text under black boxes or hidden on blank areas is still readable, and make a properly redacted copy.
Free, with no sign-up and no watermark. The file is processed in your browser and never uploaded.
Many "redacted" PDFs only have black rectangles drawn over text that is still in the file. This checker renders each page and tests every character: text sitting under a dark box is reported as recoverable, with the exact words it found, and text that is invisible or whited out on a blank area is listed separately. Problem spots are outlined in red on the pages.
If anything is found, one click creates a properly redacted copy.
Step by step
- Upload the PDF: Any PDF you received or are about to send.
- Check: Click Check Redactions and read the verdict.
- Review findings: Each finding shows the page and the text that can still be extracted.
- Fix: Optionally tick Also remove the invisible / whited-out text, then click Create Properly Redacted Copy.
Handy for
Before you publish
Verify a redacted document really hides what it should.
Due diligence
Check documents received from others for accidental leaks.
Training
Show colleagues why drawing boxes isn't enough.
After using other software
Confirm that a third-party redaction actually removed the text.
Good to know
Invisible text is normal in scanned PDFs that have been OCR'd — it isn't always a problem.
Run the check again on the fixed copy; it should come back clean.
Questions
Are my files uploaded anywhere?
No. The file is read and processed by JavaScript running in your browser tab. Nothing is sent to a server, and the result is created on your device.
How does it decide text is hidden?
It renders the page and measures each character's area. A flat dark area means the character is under a box; a flat blank area means it's invisible or whited out.
Can it find hidden images?
No. It checks text only.
Does it change my file?
Not unless you click the button to create a redacted copy.
Further reading
- How to Redact a PDF Properly, Not Just With Black Boxes — Black boxes leave text in a PDF. True redaction rebuilds the page so the content is gone; find personal data automatically and test the file before sending.
More Protect & Redact tools
- Check a PDF for Hidden Data — List a PDF's metadata, form data, attachments and scripts, and find emails, phones, PAN, Aadhaar or card numbers.
- SHA Hashes for Files — Compute SHA-256, SHA-384, SHA-512 and SHA-1 hashes of a file and compare them against a hash you paste.
- Add a Password to a PDF — Require a password to open a PDF using AES-256 or AES-128, and optionally restrict printing or copying.
- Remove a Known PDF Password — Enter the password you know and save a copy of the PDF that opens without one, with text and links kept.
- Allow Printing & Copying in a PDF — Lift print, copy and edit restrictions from a PDF you're allowed to change, keeping its text and quality.
- Find & Redact Personal Data — Find emails, phones, PAN, Aadhaar, cards, IFSC, GSTIN and IBAN in a PDF, review each match, and redact it.