How to redact a PDF properly, and check that it worked

By the PdfDady team · Updated 12 November 2026 · 6 min read

Redact PDFBlack out names, numbers and areas in a PDF so they are really removed. Free, in your browser — files aren't uploaded.

Drawing a black box over text in a PDF does not remove the text. The words are still in the file, underneath the box, and anyone can copy them out or delete the box. Proper redaction removes the text itself, and then you check the result before sending it.

Our Redact PDF tool does real redaction in your browser: every page you mark is rebuilt as an image with the marked areas filled black, so the original text on that page is not in the new file. This guide explains why the common methods fail, how to redact properly and how to check.

Why a black box isn't redaction

A PDF page is built in layers. Text is stored as actual characters, with fonts and positions. A rectangle you draw in a PDF editor, a black highlight, or a shape added as a comment sits on top as another layer. It covers the words on screen and in print, but the characters are still in the file.

That means someone can:

select the area and copy it, then paste the hidden text into a note,
search the PDF for a number and find it under the box,
open the file in an editor and move or delete the box,
run it through any text extraction tool, which ignores the box completely.

This is not a rare edge case. The US National Security Agency published a guide on safe redaction because covering text with black is, in its words, "the most common mistake". In 2009, for example, a US airport security manual was posted online with blacked-out sections that readers could reveal simply by copying the text into another program.

The same problem applies to other tricks people use: changing the text colour to white, cropping the page edge where an account number sits, or putting a sticker image on top. All of them hide, none of them remove. Cropping in particular only hides content, as our guide on cropping PDF margins explains.

Redact a PDF step by step

Open Redact PDF and add your file (one PDF, up to 100 MB). Each page appears large enough to mark.
Mark what to hide. Either drag boxes over areas, or type a word, name or number and press Mark all to mark every match on every page.
Use the presets for common details. They find Aadhaar numbers, PAN, phone numbers and email addresses. The Aadhaar preset can mark only the first 8 digits, leaving the last 4 visible, which is the masked format UIDAI itself uses.
Check every page. Remove any wrong mark with its × button. Scanned pages need boxes drawn by hand, because search can't read text in a picture.
Press Redact and download redacted.pdf.

Pages without marks are copied as they were, with their text still selectable. Marked pages become images at 200 DPI, so text on those pages can no longer be selected or searched. That is the trade-off that makes the redaction permanent.

What to redact, and what people forget

The obvious items are account numbers, Aadhaar and PAN numbers, phone numbers and addresses. Look also for the places where the same details hide a second time:

Headers and footers. Bank statements often repeat the account number on every page.
Small print. Customer IDs, reference numbers and branch codes near the bottom of a page.
QR codes and barcodes. These can encode the same details as the text. If you are hiding the details, cover the code too.
Signatures and photos if the recipient doesn't need them.
Names of other people, such as joint account holders or family members on a ration card.
File names. Rahul_Aadhaar_1234-5678-9012.pdf gives away what you blacked out. Rename the file before sending.

Never assume a redaction worked. These three checks take a minute.

Search for it. Open redacted.pdf and use Find (Ctrl+F, or the search icon in a phone PDF app) for the number or name you removed. It should find nothing.
Try to copy it. Drag across the black box and try to copy. On a redacted page there is no text to select.
Look at it zoomed in. Make sure each box fully covers what it should, including the tops of tall letters and the ends of long numbers.

Then check the file's details. Every PDF carries metadata such as a title, author and the program that created it, and sometimes the title is the very thing you wanted hidden, like a customer's name. Redact PDF replaces the document's details with a generic title. To see or clear the remaining fields (author, keywords, dates and so on), run the file through Edit PDF Metadata and press Remove all metadata.

Problems and fixes

Search didn't mark anything on a scanned document. Scans are pictures of text, so there are no words to find. Draw the boxes by hand on every page.

Mark all found too much. Searching for a short number like 2024 also marks dates and page references. Remove the extra marks one by one, or search for a longer, more specific string.

The redacted pages look softer than before. They are now images at 200 DPI. That is sharp enough to read and print, but text won't look as crisp as the original when zoomed far in.

The file got bigger. Pages stored as images can take more space than pages of text. If you need it smaller for an upload, use Compress PDF afterwards. Compressing doesn't undo the redaction.

You need to share the same document with several people. Keep the original private, and redact a separate copy for each purpose. A loan agent may need your address, while a club membership form doesn't.

When to use something other than redaction

A whole page shouldn't be shared. Delete it with Remove PDF Pages rather than blacking it out.
You want to limit reuse, not hide anything. A visible "For KYC only" stamp may be the right tool. See our guide on watermarking documents before sharing.
The whole document is sensitive and the recipient needs all of it. Redaction isn't the answer. Send it with a password instead, as explained in how to password protect a PDF.

Questions people ask

Is redaction the same as a black highlighter in a PDF app?

No. A highlight or shape is drawn on top and the text stays underneath. Redaction removes the text from the file.

Can redacted text be recovered?

Not from a page redacted with this tool, because the original text on that page isn't in the new file. Your original file still has everything, so keep it private or delete it.

Can I mask my Aadhaar number in a PDF?

Yes. Use the Aadhaar preset that keeps the last 4 digits. If you are downloading a fresh e-Aadhaar, UIDAI also offers a masked version directly.

Is my PDF uploaded?

No. The redaction happens in your browser and the file stays on your device.

Sources

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