Why You Need to Black Out Text in PDFs
There are plenty of reasons you might need to black out — or redact — text in a PDF. Maybe you are sharing a contract but want to hide personal details. Maybe you are sending a medical record and need to remove sensitive information. Or perhaps you are publishing a document that contains confidential business data.
The problem? Most people just draw black boxes over the text in a basic PDF viewer and assume it is redacted. That is not redaction. Anyone can move or delete those boxes and see what is underneath. Real redaction removes the text permanently.
This guide covers five free methods that actually remove the text — not just cover it up.
Method 1: Use an Online Redaction Tool
The fastest way to black out text in a PDF is using a free online redaction tool. Here is how:
- Go to a free online PDF redaction tool (like PDF24, Sejda, or Smallpdf)
- Upload your PDF file
- Select the text or areas you want to redact
- Click “Apply Redaction” or “Black Out”
- Download the redacted PDF
Pros: No software to install, works on any device, fast for single documents.
Cons: You are uploading sensitive data to a third-party server. If privacy is critical, consider an offline method instead.
Best Free Online Tools for Redaction
- PDF24 Tools — Completely free, no watermarks, processes files on their servers in Germany. Offers a proper redaction feature.
- Sejda PDF — Free for documents up to 200 pages or 50MB. Clean interface with a dedicated redaction tool.
- Smallpdf — Free tier available, but adds watermarks on the free plan.
- Google Docs workaround — Convert PDF to Google Docs, replace sensitive text with black highlight, export back to PDF. Clunky but works.
Method 2: Redact with Adobe Acrobat Reader (Free)
Adobe Acrobat Reader is free and available on Windows, Mac, and mobile. However, the free version has limitations when it comes to redaction.
What the Free Version Can Do
- Add black highlight annotations over text (not true redaction)
- Add black rectangles as comments or shapes
What You Actually Need
True redaction — permanently removing text — requires Adobe Acrobat Pro (paid). If you only have the free Reader, the annotation method will cover text visually but the underlying text is still searchable and copyable.
If you need true redaction and cannot pay for Pro, use one of the other methods in this guide instead.
Method 3: Use Mac Preview (macOS Only)
If you are on a Mac, Preview has a built-in redaction tool that permanently removes text.
Steps:
- Open your PDF in Preview (double-click the file)
- Click the Markup Toolbar button (pen icon) if it is not already visible
- Click the Redact button (it looks like a marker with a line through it)
- Select the text you want to redact
- The selected text is permanently removed and replaced with a black bar
- Save the file (File > Save)
Important: Mac Preview redaction is permanent. Once you save, the redacted text cannot be recovered. Always work on a copy of your original document.
This method works on macOS 10.14 (Mojave) and later. Older versions of Preview do not have the redaction tool.
Method 4: Use LibreOffice Draw (Free, Cross-Platform)
LibreOffice is a free, open-source office suite available for Windows, Mac, and Linux. Its Draw application can open PDFs and let you redact text.
Steps:
- Download and install LibreOffice from libreoffice.org if you do not have it
- Open LibreOffice Draw
- Go to File > Open and select your PDF
- Select the text you want to redact
- Delete it or draw a filled black rectangle over it
- Export as PDF: File > Export As > Export as PDF
Note: LibreOffice Draw does not have a dedicated redaction tool. You need to manually delete the text or cover it with a shape. For true redaction, delete the text rather than covering it.
Method 5: Redact on Mobile (iPhone and Android)
Need to redact a PDF on your phone? Here are the best free options:
iPhone — Using the Files App
- Open the PDF in the Files app
- Tap the markup button (pen icon)
- Use the black highlighter or shape tool to cover text
- Save the file
Limitation: This covers text visually but does not remove it. For true redaction on iPhone, use a dedicated app like PDF Expert (free tier available).
Android — Using Google Drive + Google Docs
- Upload the PDF to Google Drive
- Open it with Google Docs (it will convert)
- Replace sensitive text with black highlights or XXXX placeholders
- Download as PDF
Best Mobile Apps for Redaction
- PDF Expert (iOS) — Free tier includes basic redaction
- Xodo PDF (Android/iOS) — Free, can black out text areas
- Adobe Acrobat Reader Mobile — Free for viewing and annotating, redaction requires subscription
Covering vs. Redacting: Know the Difference
This is the most important thing in this entire guide:
| Covering Text | True Redaction |
|---|---|
| Places a black shape over text | Permanently removes the text data |
| Text is still searchable | Text cannot be searched or copied |
| Shape can be moved or deleted | Cannot be reversed after saving |
| Not suitable for legal/compliance | Meets legal and compliance standards |
| Free in most tools | May require specific tools |
If you are redacting sensitive information for legal, medical, or compliance reasons, you must use true redaction. Covering text with a black box is not secure and could lead to data leaks.
Tips for Effective PDF Redaction
- Always work on a copy — Keep the original unredacted file safe. Redaction is permanent.
- Check for metadata — PDF files contain metadata (author, creation date, edit history) that may reveal information. Use a metadata cleaner.
- Search the redacted file — After redacting, try searching for the redacted terms. If they show up, the redaction did not work.
- Check hidden layers — Some PDFs have multiple layers. Make sure you redact all layers, not just the visible one.
- Flatten the PDF — After redacting, flatten the PDF to merge all layers and remove any hidden content.
- Test with copy-paste — Try selecting and copying text from the redacted areas. If you can copy the text, it is not truly redacted.
When to Hire a Professional
For high-stakes redaction — legal discovery, government documents, HIPAA compliance, or FOIA requests — consider using professional redaction software or services. Tools like Adobe Acrobat Pro, Redact-It, or specialized legal software provide audit trails and compliance guarantees that free tools cannot match.
Quick Summary
- Fastest method: Online redaction tool (PDF24, Sejda)
- Best free desktop method: Mac Preview (macOS) or LibreOffice Draw (any OS)
- Best mobile method: PDF Expert (iOS) or Xodo PDF (Android)
- For legal/compliance: Use true redaction, not just black boxes
- Always test: Search and copy-paste to verify redaction worked
Black out text the right way, and your sensitive information stays private. Do it the wrong way, and you might as well not bother.