How to Redact a PDF

Redaction permanently removes sensitive content from a PDF so it cannot be recovered. Done wrong, it is one of the most expensive mistakes in document handling — law firms, government agencies, and companies have all been burned by "redaction" that turned out to be a black rectangle over text that was still in the file. This guide explains what true redaction is, why the obvious approach fails, and which tools do it correctly. It is also honest about IXPDF: we cannot do redaction today, and we will not ship a fake redaction tool.

True redaction vs. covering with a rectangle

There are two things people call "redaction." Only one is real:

• Covering with a black rectangle (NOT redaction). You draw a black box over the text in a PDF editor. The text is still in the file — the box is just on top of it. Anyone who removes the box, selects the text under it, or copies the file's text content can read what was "redacted." This has caused real-world leaks: the US DOJ released a document with "redactions" that were black rectangles over still-selectable text, and journalists copied the text out.
• True redaction. The tool removes the text (or image) from the PDF's content streams entirely. The characters are gone from the file. There is nothing to select, copy, or recover. This is the only kind of redaction that is safe for sensitive content.

What true redaction does to the file

When a true redaction tool applies the redaction, it:

1. Removes the text characters from the page's content stream.
2. Removes the image data if redacting an image region.
3. Fills the redacted region with a solid color (usually black) so the area is visibly marked.
4. Optionally removes metadata and hidden layers that could leak the redacted content.
5. Rewrites the PDF so the removed content is not recoverable from the file's structure.

After true redaction, the file is smaller (the content is gone) and the redacted region is genuinely empty — not just covered.

The danger of incomplete redaction

Incomplete redaction is worse than no redaction because it creates a false sense of security. Common failure modes:

• Text under a black box. The classic failure. The box is an annotation; the text is still in the content stream.
• Redacted text in metadata. You redact the body but the author, title, or keywords metadata still contains the sensitive name. True redaction tools offer to sanitize metadata too.
• Redacted text in hidden layers. Some PDFs have optional content groups (layers) that viewers can toggle. Redacting the visible layer does not redact the hidden one.
• Redacted text in embedded fonts. The character glyphs may remain in the embedded font subset even after the text is removed from the content stream. A skilled attacker can sometimes recover text from font subsets.
• Redacted image not removed. Drawing a black box over an image leaves the image in the file. A true redaction tool removes the image data.

Tools that do true redaction

1. Adobe Acrobat Pro (paid, the reference tool)

Acrobat Pro has a dedicated Redact tool (Tools > Redact). Select text or images to redact, or useFind Text to redact all occurrences of a word or phrase. ClickApply and Acrobat removes the content from the file. It also offers to sanitize metadata, hidden layers, and embedded data. This is the tool to use for legal, government, or medical documents. Acrobat Standard and the free Adobe Reader cannot redact — only Pro can.

2. Preview (macOS, free, NOT true redaction)

Preview's Markup > Shapes > Rectangle with a black fill is not redaction. It draws a black annotation over the text; the text is still in the file. We mention Preview here only to warn against using it for redaction. If you only have a Mac and no Acrobat Pro, use the command-line tools below or accept that you cannot safely redact with Preview.

3. Command-line tools (free, for advanced users)

There is no single "redact" command in qpdf or ghostscript, but you can combine tools: use pdftotext to find the text, then a Python script with pypdf and reportlab to remove the content stream and overlay a black rectangle. This is error-prone and we do not recommend it for high-stakes redaction. For anything sensitive, use Acrobat Pro.

Step-by-step: redact a PDF with Adobe Acrobat Pro

1. Open the PDF in Adobe Acrobat Pro.
2. Go to Tools > Redact.
3. Mark redactions: drag to select text or images, or click Find Text to redact all occurrences of a word or phrase.
4. Review the marked regions in the document.
5. Click Apply in the secondary toolbar.
6. Acrobat asks if you want to Sanitize & Remove Hidden Information. Click OK — this removes metadata, hidden layers, and other potential leaks.
7. Save the redacted PDF with File > Save.
8. Verify: reopen the file, try to select the redacted area, and run Find Text on a term that was redacted. It should find nothing.

What to redact (and what to just hide)

Not everything needs true redaction. Use this guide:

• Redact (remove from file): names, addresses, phone numbers, email addresses, Social Security numbers, bank account numbers, medical record numbers, dates of birth, signatures, and any content under a protective order or grand jury seal.
• Hide (cover with a rectangle, but only if the file will not be shared): draft annotations, internal notes that will be removed before sharing. But if the file leaves your control, redact instead.
• Strip metadata: author, title, subject, keywords, creation date, modification date, producer, creator. Use IXPDF'sEdit Metadata tool to clear these before sharing.

Common mistakes

• Drawing a black rectangle and calling it redaction.The text is still in the file. This is the most common and most dangerous mistake.
• Redacting the body but not the metadata. The sensitive name may still be in the document's Author or Title field. Sanitize metadata too.
• Not verifying. After redaction, reopen the file and try to select or search the redacted text. If you can find it, the redaction failed.
• Using a screenshot or image of the redacted document.If you take a screenshot of a "redacted" PDF and share the screenshot, you are safe — but only if the screenshot does not capture the text under the boxes. This is a workaround, not a real workflow.
• Trusting a "free online redaction" tool with sensitive content. The file is uploaded to a server before redaction. For legal or medical content, use a local tool.
• Redacting only the visible page. Some PDFs have hidden layers or attachments. A true redaction tool sanitizes all of them; a black rectangle does not.