How to Redact a PDF: Black Out Sensitive Information
Hiding a name or number in a PDF sounds easy, and is surprisingly easy to get wrong. This guide explains how redaction fails, how our Redact PDF tool makes it permanent, and what to check before you share the file.
The mistake that has leaked secrets
Most people who want to hide something in a PDF draw a black rectangle over it, or paint it black with a highlighter tool, then save the file. The text still looks hidden. But in many files the original text is still stored under the box. Anyone can drag across the area, copy the hidden words and paste them somewhere else. Organisations, law firms and government departments have all made this mistake and published documents with the "hidden" text still readable.
Real redaction means the information is gone from the file, not just covered up.
How our Redact PDF makes it permanent
Redact PDF does not leave the text underneath. When you save, every page that has a box on it is redrawn as a picture with the black boxes burned in, and that page in the new PDF is built from the picture. The original text on that page is not in the new file, so the text under a box cannot be selected, copied or searched, because it is not there to find.
The same step has side effects you should understand before you start:
- Redacted pages are flattened. On pages with a box, none of the text can be selected or searched afterwards. Pages without boxes are left exactly as they were and stay searchable.
- The file may be larger, because a page picture is heavier than text.
- Document properties are removed. Metadata such as the original title and author is not carried into the new file.
- It is irreversible. Keep your original in a safe place, because you cannot get the hidden information back from the redacted copy.
Step by step
- Open Redact PDF and choose your file.
- To hide a word or number wherever it appears, type it in Find & redact text and press Find & mark all. Every match on every page is marked. Spaces inside numbers are optional, so 1234 5678 9012 also finds 123456789012.
- To hide anything else, press and drag with your mouse or finger to draw a box over it. Make each box slightly larger than the text so that no edge shows.
- Move through the pages and check every one, including the last. Select a box to move, resize or delete it.
- Press Redact & download. The new file downloads with -redacted added to its name.
What to redact
The tool does not decide what is sensitive. Find & redact marks every match of a word or number you type, which is ideal for an Aadhaar, PAN or account number that repeats; everything else you mark yourself. Think about the categories before you start:
- Names of people who should not be identified, including in headers and footers.
- Government ID numbers, tax numbers, account and card numbers.
- Home addresses, phone numbers and email addresses.
- Dates of birth and signatures.
- Photographs and barcodes or QR codes that encode personal data.
- Financial figures, salaries and bank balances.
- Names that repeat later in the document, such as in a signature block or on a page footer.
The safe way to check your work
Do not trust the preview alone. After you download the redacted copy, open it in a PDF viewer and run these checks:
- Try to select the text under a box by dragging across it. Nothing should highlight. On redacted pages no text at all can be selected; other pages keep their text.
- Use the viewer's search to look for a sensitive word, such as a surname or an account number. There should be no matches.
- Scroll through every page at a large zoom and look for edges of text peeking out around boxes.
- Check the file name. A name like "Loan-for-Priya-Sharma.pdf" gives the secret away even if the content is hidden. Rename the file.
Redact versus crop versus delete
Several tools seem to hide content, but they work differently.
| Tool | What it does | Safe for hiding secrets? |
|---|---|---|
| Redact PDF | Burns boxes into the marked pages and rebuilds them as pictures | Yes, when you cover every item |
| Crop PDF | Changes the visible area of each page | No. The trimmed content may still be in the file |
| Delete PDF pages | Leaves whole pages out of a new file | Yes, for entire pages |
| Watermark | Adds text over the page | No. It is a label, not a cover |
Worked example: sharing a bank statement
A person applying for a visa needs to show six months of income but does not want to reveal individual transactions. They first delete the final page, which lists unrelated information, using Delete PDF pages. Then they open the statement in Redact PDF, type the account number into Find & redact so it is marked on every page, and draw boxes over the merchant names. After exporting, they search the new file for the account number (no result), try to select text (impossible), and look at each page at full zoom. They rename the file to "income-statement-redacted.pdf" and send it.
A few limits to be aware of
Redacted pages become pictures. If a released document must stay fully searchable, such as a public records release, use specialist redaction software that removes only the covered text, and have the result reviewed. If you only need the redacted pages to be searchable again for your own use, run OCR PDF on the redacted copy; the hidden text stays gone because it is no longer in the file.
Find & redact only finds text that is stored as text. In a scanned page, the words are part of a picture, so draw boxes by hand there.
Nothing replaces your own care. A hidden name on page 2 may appear again on page 9, so go through the whole document.
Troubleshooting
Find & redact finds nothing. The page may be a scan, or the number may be split across lines. Draw the boxes by hand.
The result is large. Redacted pages are pictures. Delete pages you do not need first, and see the size guide.
The tool asks for a password. Type the password you use to open the PDF. It is used only in your browser.
The tool could not read my file. It may be damaged. Try Repair PDF first.
Frequently asked questions
Is black-box redaction in other programs safe?
Not always. In many programs the original text stays under the box. Our tool rebuilds each redacted page as a picture, so the covered text is not in the output.
Can I search the redacted PDF?
Pages without redactions stay searchable. Redacted pages are pictures; run OCR PDF on the copy if you need them searchable again.
Can it find Aadhaar or account numbers automatically?
Type the number or word into Find & redact and every match is marked. The tool does not guess what is sensitive on its own.
Can the redaction be undone?
Not from the redacted file. Keep your original somewhere safe.
Keep reading
- Are Online PDF Tools Safe? What to Check Before You Upload
- How to Sign a PDF Online for Free (Step by Step)
- How to Delete, Rotate and Reorder PDF Pages Online
Written by the iLoveDocuments team and checked against how the tools behave today. Spotted a mistake? Tell us and we will fix it. See our editorial standards.