How to Redact a PDF for Free (Don't Just Put Black Boxes Over Text)

In 2021, a law firm redacted a legal filing and posted it online. The document had black rectangles over sensitive names and addresses. But someone clicked and dragged over those black boxes, selected the text, and copied it. The "redacted" information was fully accessible.

This happens all the time. People think putting a black rectangle over text makes it unreadable. It doesn't. It just covers it visually. The underlying text is still there, waiting to be revealed.

Real redaction removes data. It doesn't just hide it. Let me show you the difference and how to actually redact PDFs properly.

Why Most PDF Redaction is Fake

Here's the thing about PDFs: they work in layers. You have the text layer, the image layer, the annotation layer, and others. When you draw a black rectangle over text using a standard PDF annotation tool, you're adding something to the annotation layer. The text layer underneath is still fully intact.

In most PDF readers, you can:

• Select the black rectangle and delete it
• Highlight the text through the rectangle
• Copy and paste the "hidden" text
• Export the PDF as a different format
• Use OCR tools that read through the overlay

I've seen people get creative. They use black bars, white bars, solid shapes, even images that match the background color. None of it matters if the text is still there in the document structure.

What Proper Redaction Actually Does

Real redaction removes the information from the document entirely. It doesn't cover it — it deletes it. The redacted area is replaced with a blank space or a solid block that's part of the document itself, not an overlay.

Think of it like this:

• Fake redaction: Drawing a mustache on a photo. You can still see the mouth under it.
• Real redaction: Using Photoshop to erase the mouth and replace it with skin texture.

The key difference is that with real redaction, there's nothing left to recover. No hidden text, no embedded data, no metadata references. It's gone.

When Do You Actually Need Redaction?

I don't want to be alarmist. Not every document needs professional-grade redaction. Here's when it genuinely matters:

Legal Filings and Court Documents

Courts have specific rules about redaction, and they're serious about them. Personal identifiers, minor names, trade secrets — these all need proper redaction. In some jurisdictions, improper redaction can get you sanctioned.

Medical Records

HIPAA is no joke. Patient names, addresses, diagnosis codes, insurance information — anything that could identify a patient needs to be permanently removed. A "black box" won't cut it if an audit comes.

Financial Documents

Bank statements, tax returns, payroll records — these contain account numbers, SSNs, and financial details that identity thieves love. Real redaction is the difference between "oops, I forgot to block that" and a full-blown security incident.

Business Contracts and Proposals

Sometimes you need to share a contract with certain information removed — maybe pricing, vendor names, or technical specs you consider proprietary. Again, fake redaction leaves you exposed if someone checks.

Government and FOIA Requests

Freedom of Information Act responses often need to redact classified information, ongoing investigation details, or personal privacy data. Government agencies learned this the hard way after multiple high-profile failures.

How to Redact a PDF Properly

Method 1: Adobe Acrobat Pro

Adobe's redaction tools are the gold standard. They've had a couple of decades to get this right. Here's how to use them:

1. Open your PDF in Acrobat Pro
2. Go to Tools → Protect → Redact
3. Mark the areas you want to redact by drawing rectangles
4. Click Apply to permanently remove the data

Acrobat Pro has some nice features:

• Search and redact: Auto-redact every instance of a name, email, or SSN
• Redaction codes: Add codes like "PRIVILEGED" or "CONFIDENTIAL" to redacted areas
• Page ranges: Redact entire pages or specific ranges
• Preview before applying: See what will be removed before committing

The downside is, again, Adobe Acrobat Pro costs money. About $20/month for the individual plan.

Method 2: Using PDF-XChange Editor

PDF-XChange Editor is a Windows application with solid redaction tools. The free version has basic redaction; the paid version adds advanced features. The process is similar to Acrobat:

1. Open the PDF
2. Select the redaction tool
3. Mark areas to redact
4. Apply the redaction (this permanently removes content)

I've used PDF-XChange for years. It's faster than Acrobat for many tasks, and the one-time purchase for the Pro version is way cheaper than Adobe's subscription model.

Method 3: Using LibreOffice Draw

This is a free option that works, but it's a bit hacky. Here's the approach:

1. Open the PDF in LibreOffice Draw
2. Draw white rectangles over the text you want to redact
3. Export as PDF
4. Reopen the exported PDF to verify the text is gone

The trick is that when you export to PDF, LibreOffice renders everything as a flat image. The white rectangles get "baked in" and the original text is gone. It works, but:

• You can't undo the redaction afterward
• You lose the ability to edit anything in the document
• Complex PDFs sometimes break when opened in Draw
• It's not as trustworthy as dedicated redaction tools

Method 4: Print to PDF

Here's the low-tech method that actually works for simple documents:

1. Use the annotation tool in any PDF editor to cover sensitive areas
2. Print the PDF to a new PDF (or use "Save as" with flatten options)
3. Verify the text is actually gone

On Mac, you can use Preview to draw shapes over text, then print to PDF. On Windows, many PDF editors have a "flatten" or "burn annotations" feature that permanently merges annotations into the document content.

Our PDF flatten tool does exactly this — it merges all layers into a single flat document. After flattening, annotations become part of the document itself and can't be removed.

Method 5: Using Command Line Tools

For the technically inclined, there are command line options:

• Redact-cli: A Node.js tool for redacting PDFs
• QPDF: Can remove content by object ID (advanced usage)
• Ghostscript: Can flatten and sanitize PDFs

These are powerful but require understanding PDF internals. Not for casual users.

Redaction Checklist

Before you release a redacted document, verify it actually worked:

1. Try to select and copy the "redacted" text. If you can copy it, it's not redacted.
2. Use the text selection tool to drag across the whole document. Check for hidden text.
3. Search for terms you redacted. If the document was supposed to have "Smith" removed but you can still find it, something went wrong.
4. Open in different PDF viewers. Adobe Acrobat, Preview, Chrome, Edge — test in at least two.
5. Try exporting to a different format. Export to Word or text. If the redacted information appears, the redaction failed.
6. Run exiftool on the file. Check that metadata doesn't contain the redacted information. (See my guide on removing metadata.)

Famous Redaction Failures

You're not alone if you've messed this up. Here are some public redaction disasters:

The Paul Manafort Affidavit

In 2018, a redacted court filing in the Paul Manafort case was released. Journalists discovered that the redacted names could be revealed by copying and pasting into a plain text editor. The redaction layer didn't actually remove anything.

New York Police Department Documents

In 2020, the NYPD released body camera footage documents with blacked-out names. Someone simply changed the background color to white, and the names appeared. The redaction was just a foreground color overlay.

Various FOIA Failures

Government agencies regularly fail FOIA redaction audits. A 2016 study found that improper redaction was the second most common mistake in released documents, after privacy violations.

Advanced Redaction Considerations

Document Versions

A redacted PDF might still have edit history, undo information, or previous versions embedded. This is especially common with PDFs created from Word or other editing software. Real redaction tools handle this; fake redaction doesn't.

Hidden Text Layers

Some PDFs have OCR text layers under the visible content. You might redact the visible text but the OCR layer still contains it. Proper redaction tools remove all layers.

Comments and Annotations

Comments, reviewer notes, and other annotations can contain sensitive information. Make sure to check for these before redacting — and redact or remove them too.

Embedded Images

Sometimes sensitive information is in an embedded image rather than text. You can't just redact text layers and be done. Check images for embedded text, metadata, or other data.

Patterns and Formats

Redacting an email address but leaving the phone number might reveal the person through other means. Think about what a motivated person could deduce from what remains.

What About Digital Signatures?

Once you redact a PDF, any digital signatures become invalid. That makes sense — you've modified the document. If you need to maintain a valid signature, you have to:

• Redact before signing
• Re-sign after redaction (which defeats the purpose)
• Accept that the signature won't verify

This is a known issue in legal workflows. It's why many courts require redacted documents to be submitted separately from originals.

A Note on OCR and Accessibility

Proper redaction removes text that screen readers can access. That means fully redacted documents may not be accessible to people using assistive technology. This is a necessary tradeoff for security, but it's worth being aware of if you need to maintain accessibility compliance for non-redacted content.

Quick Tips

• Always verify redaction before sharing. Always.
• Test by opening the document in multiple PDF viewers.
• Try to copy and paste the "hidden" content.
• For high-stakes redaction, use dedicated tools like Acrobat Pro.
• Keep the original unredacted document in a secure location.
• Consider metadata removal as part of the redaction process.
• If in doubt, over-redact. Better to remove too much than too little.

The Bottom Line

Redaction is one of those things that seems simple but isn't. Drawing black boxes over text is the most intuitive approach — and it's also completely wrong.

Real redaction removes data. It doesn't hide it. That's the whole point. If someone can access what you covered up, it's not redacted.

For low-stakes situations, flatten or print-to-PDF methods work well enough. For anything legal, medical, financial, or otherwise sensitive, use proper redaction tools. Verify the results. Trust but verify, as the saying goes.

And remember: once you apply redaction, it's permanent. Save a backup of the original.