August 2026 • 6 min read

How to Redact a PDF Properly (Not Just Cover It Up)

Every so often a story goes around about a government agency, a law firm, or a company that "redacted" a document by drawing black rectangles over the sensitive parts, only for someone to select the text underneath, copy it, and paste it somewhere else. The secret was never actually removed. It was just hidden behind a shape.

This happens constantly because most people, understandably, think a black box equals redaction. It doesn't. Real redaction means the underlying content is gone, not painted over. We just added a proper Redact tool to PDF Compresso, so it felt like the right time to explain the difference properly.

The Problem With Fake Redaction

If you open a PDF in a basic editor and draw a black rectangle on top of a paragraph, here is what actually happened: you added a new shape to the page. The text that was there before is still there, sitting in exactly the same place, just visually hidden underneath your shape.

Anyone who opens that file can select all the text on the page, or use a "select all" and copy command, and the hidden text comes along with everything else. Some PDF readers will even show it in a text search. The document looks redacted to the eye. It is not redacted to the file itself.

Quick test: if you can select the text underneath a black box with your cursor, or find it with Ctrl+F, it has not been redacted. It has been decorated.

What True Redaction Actually Means

Real redaction has to remove the content at the data level, not the visual level. There are a few ways to do this properly, but the most reliable approach, and the one PDF Compresso uses, is to flatten the affected page into a flat image with the redaction boxes burned directly into the pixels.

Once a page has been flattened this way, there is no separate text layer to select, no hidden object underneath the box, and nothing to extract. The original content simply no longer exists in the file. Pages that don't have any redactions on them are left completely untouched, keeping their original text layer, searchability, and image quality.

How to Redact in PDF Compresso

  1. Open PDF Compresso and go to the Convert & Security page
  2. Select the Redact tab
  3. Upload the PDF you want to redact
  4. Click and drag to draw boxes over every piece of content you want removed
  5. Review each box carefully, since this step is permanent
  6. Click Apply, then download your redacted PDF

Behind the scenes, any page with a redaction box on it gets flattened to an image with the box burned in. Pages without redactions keep their original quality. The whole process runs locally, so the document with the sensitive content never leaves your device.

What You Lose (and Why It's Worth It)

There is a small trade-off. Once a page is flattened to an image, the text on that specific page stops being selectable or searchable, since it is now pixels rather than characters. For the rest of the document, nothing changes. Given the alternative is content that only looks removed, this is a fair price for content that is actually, permanently gone.

When You Should Use Redaction

  • Medical records, removing patient identifying information before sharing for research or billing
  • Financial statements, blacking out account numbers before sending to a third party
  • GDPR compliance, removing personal data before a document leaves your organisation
  • FOIA or freedom of information responses, redacting exempt sections before release
  • Legal documents, removing privileged or confidential content before disclosure

A Few Things to Get Right

Keep the Original Somewhere Safe

Redaction in PDF Compresso is permanent by design. That's the whole point. It does mean you should always keep a backup copy of the original file in a secure location before you redact anything, in case you need the unredacted version again later.

Check Every Box Before You Apply

Take the extra thirty seconds to look over each redaction box before confirming. It is much easier to catch a missed sentence now than after the file has already been sent.

Don't Forget Metadata

Redacting the visible content is only part of the picture. PDFs can carry metadata such as author names, creation software, and edit history. If any of that is sensitive too, PDF Compresso's Metadata tool lets you review and clear it separately before sharing the file.

Check the File Size Afterward

Flattened pages are images, so a heavily redacted document can end up larger than the original. If that matters for email or upload limits, running the file through the Compress tool afterward brings it back down without touching your redactions.

Redact With Confidence

True redaction, processed entirely on your device. No uploads, no shortcuts.

Get PDF Compresso - £24.99 (one-time)

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