PDF redaction checker Free, no sign-up
Before you publish or hand over a redacted PDF, check whether anything readable survives under the blackouts — a shape laid on top, text turned white, concealment by an annotation.
The file never leaves this device
Reading and checking happen entirely inside your browser. There is no code on this page that sends a file anywhere. The library, character maps and fonts are served from abyo.net rather than from an external network.
To verify: leave this page open, disconnect, then add your PDF. It still works.
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Several files at once is fine
What this tool does not check
- It does not read the text inside images.
- For a PDF that was printed and scanned again, it cannot examine what is in the image.
- It does not judge whether everything that should have been blacked out was. It checks whether what WAS blacked out is really gone.
What is checked, and how it is judged
How this tool judges is published. The table and thresholds below are the substance; the rules in full, and the test documents, are in the public repository. A document redacted properly comes back clean whatever produced it.
The rules and the test documents are published. Tests confirm that a document redacted properly comes back clean whatever produced it, using real files redacted with Acrobat and with abyo PDF Editor.
The criteria and the test documents (GitHub, CC0)
| ID | What is checked | Verdict |
|---|---|---|
| A1 | Extractable text left under an opaque shape or image | Problem (needs a look when the cover is not dark, or its shape cannot be judged) |
| A2 | A bar covering only part of the text, leaving the rest visible | Problem |
| A3 | A /Redact annotation that was never applied, or text concealed by a dark annotation — a black square or a black highlight. An ordinary coloured highlighter hides nothing and is not reported | Problem (needs a look if the cover is not dark) |
| A4 | Text the same colour as its background (white text), or text outside the page or the clip | Same as background: problem. Outside: problem near a blackout, otherwise needs a look |
| A5 | Invisible text (render mode 3 or 7) under a blackout — commonly the OCR layer of a scan | Problem |
| A6 | A shape or another image laid over an image while the image data underneath is unchanged | Problem (needs a look when the cover is not dark, its shape cannot be judged, or the pixels cannot be read) |
| A7 | An earlier revision left in the file by an incremental save, with different content | Problem (needs a look when the revision cannot be parsed) |
| A8 | Text left in /ActualText or /Alt in the tag tree that the page no longer shows | Problem |
| A9 | Document info and XMP, bookmark titles, attachments, values typed into form fields, XFA form data, annotation text and tooltips, a signature's signer name, reason and location, link targets that carry personal data (a mailto:, say), hidden layers, embedded thumbnails, JavaScript | Needs a look (listed with its contents) |
| A10 | No extractable text, with images covering at least 80% of the page — a scan | Needs a look |
| A11 | A password is needed to open it, so nothing inside can be examined. An encrypted file that does open is checked normally | Needs a look |
The thresholds used
- Blackout darkness
- L ≤ 0.25
- Opacity
- ca ≥ 0.95
- Size
- 3pt / 6pt
- Rectangularity
- ≥ 0.9
- Dark pixel share
- ≥ 0.95
- Text covered
- ≥ 0.85
- Partly covered
- ≥ 0.15
- Contrast with background
- < 0.15
Rules version: 1.7
Redacting properly
Whatever tool you use, doing these four things means nothing readable survives a blackout (A1-A8). A scan with no extractable text, or a file that still carries document info or attachments, comes back as needing a look even when nothing was left behind.
- Delete the text from the document instead of covering it
- Rewrite image pixels instead of laying a shape over them
- Remove the OCR text layer and the tag tree's alternate text too
- Strip document info, attachments and hidden layers, and do not save incrementally
Who makes this tool
Published by abyo software LLC, who build abyo PDF Editor, a PDF editor for Windows that does all four of the above. Pay once, fully offline.
Terms
Decisions about publishing or releasing a document remain the user's responsibility. We do not warrant that the result is complete.
Browsers: current Microsoft Edge and Google Chrome. Firefox and Safari also work.