In January 2019, Paul Manafort's lawyers filed a redacted document with a US court. The secret parts were covered with black boxes and genuinely unreadable on screen. Then journalists selected the text, copied it, and the sentences under the boxes popped right out. It wasn't the first case and it won't be the last. That's why the answer to "how do I redact a PDF?" is not "draw a black box over it".
This guide covers the right way to redact text in a PDF, why a black box isn't enough, how to find personal data (ID numbers, IBANs, phone numbers) automatically, and the five checks to run before you send the document.
How do I redact a PDF?
- Open Redact PDF and pick the file.
- Mark what to remove: draw areas with your mouse, search for a word to mark every occurrence, or press "Find personal data" to catch it all at once.
- Choose the redaction color (black or white). Leave "Remove metadata" on.
- Redact and download.
The information inside the marked areas is permanently removed from the file. It all happens in your browser, so the information you're trying to hide never reaches a server, not even during redaction.
A note from Yeti: snow covers everything, but when it melts, what's underneath comes back. A black box is like snow. Real redaction removes the thing from the mountain altogether.
Why doesn't a black box work?
A PDF page is built in layers. The text sits on one layer; the rectangle you draw later sits on another. The box hides the text on screen but doesn't delete it from the file. The hidden information comes back like this:
- Select and copy: selecting text across the box and pasting it elsewhere is often enough.
- Search: Ctrl+F for the covered word, and the viewer finds and highlights it.
- Delete the box: if the rectangle was added as an annotation, any PDF program can select and delete it.
- Convert to text: any tool that turns the PDF into text or Word extracts what's under the box too.
Scans are sneakier still: if the document was OCR'd earlier, there's an invisible text layer behind the image. Draw a box on the image and that hidden text stays put.
What does real redaction do?
- Characters inside the area are removed from the page's content; only a rectangle is drawn in their place.
- Image pixels inside the area are painted over within the image itself; no copy of the original stays underneath.
- Annotations, form fields and drawings that fall within the area are removed.
Redact PDF does all three and checks the result before saving: if anything readable remains under a redaction, it closes the gap by turning only that page into an image. The rest of the page stays selectable and searchable.
Finding personal data automatically
Drawing boxes one by one across a long document is tiring and error-prone. Instead:
- Search for text. Type a name, an address or a case number and every occurrence gets marked. "Whole word only" stops a search for "Ann" from also marking "Annual".
- Press "Find personal data". Email addresses, phone numbers, IBANs, card numbers and ID numbers are marked in one click. ID numbers such as SSN, NINO, Steuer-ID, DNI/NIE, PESEL, CPF and Aadhaar are validated by their check digits, so invoice and order numbers aren't redacted by mistake. Names aren't part of this scan; add them with a text search.
- Draw the rest by hand. For signatures, photos, logos and anything that doesn't follow a pattern.
On scanned pages the tool recognizes the text first, so you don't need to run OCR yourself.
Information outside the page
Even if every bit of the page is properly redacted, the same information may live elsewhere in the document:
- Metadata: a name in the "Author" field, a "Title" like "J. Smith – draft warning letter".
- Bookmarks: a person's name in the table of contents.
- Comments and notes: "Should we remove this?" notes from drafting.
- Attached files: a spreadsheet or email embedded in the PDF.
- The file name itself: redacting the inside of "jane-doe-medical-report.pdf" doesn't achieve much.
Sanitize Document removes all of these in one go. Running it after redacting is a good habit.
Five checks before you send
- Search for one of the redacted words with Ctrl+F. It shouldn't be found.
- Select text across a black box and paste it into a text editor. Nothing should come through.
- Convert the file with PDF to Text and search for the hidden information.
- Check the author, title and subject fields in the document properties.
- Look for bookmarks, attachments and comments in the viewer's side panel.
All five clean? The document is ready to share.
Frequently asked questions
How do I redact a PDF for free?
Use Redact PDF. It's free, needs no sign-up, and your document is processed in your browser.
Can redaction be undone?
Not if it was done properly, and that's the point. Keep the original separately and save the redacted copy under a new name. If you redacted the wrong spot, start again from the original.
Can redacted text in a PDF be recovered?
With black-box "redactions", often yes, using the methods above. With real redaction, no, because the information is no longer in the file.
When should I use white instead of black?
When it shouldn't be obvious that something was removed, for example when clearing old details from a template. Official documents usually use black, so it's visible what was taken out.
Can I redact in Preview on a Mac?
Depending on your macOS version, Preview may offer a redaction tool, but drawing a black shape with its markup tools is not redaction. Whichever tool you use, run the five checks above before sending.
In short
A black box hides; redaction deletes. Use a tool that really removes the information, find personal data automatically, strip the metadata and run the five checks before sending. For more, see how to tell where online tools send your files.