Security & Practice · 2026

What Is True PDF Redaction? Why a Black Box Isn't Enough

A black rectangle drawn over text in a PDF looks like a redaction. It is not. The text underneath stays in the file, recoverable by anyone who knows how to select, copy, or parse the document. This distinction has caused real, public data breaches in court filings, government reports, and corporate disclosures. Here's how true redaction works and how to tell the difference.

What a black box actually does (and doesn't do)

A PDF is not a photograph. It's a structured file containing text objects, font definitions, images, vector graphics, and metadata — layered on top of each other. When you draw a black rectangle using a standard PDF annotation or markup tool, you're adding a new visual layer on top of the existing text. The text object underneath is completely untouched.

This means anyone who receives the "redacted" file can recover the hidden content by selecting the text under the box and copying it, removing the annotation layer in any PDF editor, extracting the text stream with a command-line tool, or searching the document (search hits text under the box because search reads the text layer, not the visual layer).

This is not theoretical

High-profile failures of visual-only "redaction" have exposed Social Security numbers in federal court filings, classified information in government reports, confidential financial data in SEC disclosures, and privileged legal strategy in litigation documents. In each case, the filer believed the content was removed because it was visually hidden. It was not.

How true redaction works

True redaction has two stages, and both must happen:

Marking: You identify the areas to redact — drawing boxes, searching for text patterns (a name, SSN, account number), or selecting specific passages. At this stage, nothing has been destroyed yet; the marks are a plan, not an action.
Applying (burning in): The redaction tool processes each marked page by rendering the entire page to a flat image (rasterization), with the redaction boxes drawn into the image before the original text layer is discarded. The result is a page that is visually identical to the original — minus the redacted areas — but contains no recoverable text, font data, or metadata from the original underneath the boxes.

After this process, the redacted areas are not "covered" — they are gone. The page is now an image. There is no text layer to select, copy, search, or extract. The redaction is permanent and irreversible.

What happens to the rest of the document?

A well-designed redaction tool only rasterizes the pages that actually contain redaction marks. Pages with no redactions are left completely untouched — their text remains selectable, searchable, and intact. This matters for large documents: if you redact one paragraph on page 3 of a 200-page contract, pages 1-2 and 4-200 should still have full, searchable text.

Tools that rasterize the entire document (all pages, regardless of whether they contain redactions) produce a technically secure result but sacrifice searchability across the whole document unnecessarily.

Black boxes vs. white boxes

Standard redaction uses black boxes — the visible mark signals "content was withheld here." This is the convention for privileged material, classified information, and anything subject to a protective order, where the existence of the redaction itself is part of the record.

White boxes serve a different purpose: cleanly erasing content without leaving a visible trace. This is appropriate when removing your own working notes from an exhibit copy, cleaning up margin annotations, or removing metadata that shouldn't appear in the filed version. The underlying content is destroyed just as completely as with a black box — the only difference is visual.

How to verify a redaction worked

After applying redactions, always verify before filing or producing the document:

Select test: Open the redacted PDF, click and drag across the redacted area, try to copy and paste into a text editor. If any text appears, the redaction failed.
Search test: Use your PDF viewer's search function to search for a word you know was in the redacted area. If it finds a hit on that page, the text layer is still present.
Properties check: Look at the page's properties or metadata — a truly rasterized page will show as a single image object rather than a collection of text and font objects.

Search-and-redact for names and numbers

When redacting a person's name, account number, or other repeating identifier across a long document, drawing individual boxes is slow and error-prone — missing one instance defeats the purpose. Search-and-redact tools find every occurrence across every page and mark them all at once for review before applying. This is the appropriate workflow for personally identifiable information, opposing party names under seal, and financial account numbers.

Redact for real, not for show

Exhibix uses true rasterization-based redaction with black or white boxes, search-and-redact for names and numbers, and selective page flattening that preserves searchability on untouched pages — all processed in your browser, with files that never leave your machine.

Open Exhibix

Frequently asked questions

Does drawing a black box over text in a PDF actually redact it?

No. A black rectangle drawn with a standard PDF annotation tool only covers the text visually. The original text, fonts, and metadata remain in the file's data stream and can be extracted by selecting and copying, opening the file in a text editor, or using any PDF parsing library.

What is the difference between a redaction annotation and true redaction?

A redaction annotation marks an area for redaction but doesn't remove the content until the redactions are "applied" or "burned in." True redaction is the step that actually destroys the underlying content — typically by rasterizing the affected page. Until that step happens, the annotation is just a visual overlay.

How can I verify that a redaction actually removed the text?

Open the redacted PDF, click and drag to select the area under the redaction box, then try to copy and paste it into a text editor. If any text appears, the redaction failed. You can also search for known words that were in the redacted area.

Does redaction affect the rest of the document?

With proper selective redaction, only the pages containing redaction marks are flattened. All other pages remain fully searchable, with selectable text and intact fonts. Exhibix uses this approach — pages without redactions are left completely untouched.