You need to hide a Social Security number, an address or a name in a PDF before sharing it. The quick fix is to draw a black rectangle over it and save. On screen it looks finished. The problem is that on screen is not the same as in the file.
This guide explains why a black box often fails, what real redaction means, how to test your own file in a minute, and where our free tool fits in.
Key Takeaway: Redaction is about what is left in the file, not what you can see. Always test the saved file by searching for a redacted word and copying the page text.
Why a Black Box Hides Text But Does Not Remove It
A PDF page is a stack of items: text, images and shapes. When you add a black rectangle with a markup, highlight or drawing tool, you add one more item on top. The text item underneath is not changed. Your eyes see black, but software that reads the text can still read it.
This is why a "redacted" page can often be defeated with three actions: select the area, copy, and paste into a text editor. A guide to redacting PDFs in Acrobat X hosted by Columbia University describes exactly this risk: the black box only hides the data, and copying it into another document can reveal what is underneath. A 2009 Nextgov article written after a TSA document leak lists covering text with black rectangles among the common redaction mistakes.
A Real Example: The 2019 Manafort Filing
In January 2019, lawyers for Paul Manafort filed a court document with paragraphs blacked out. According to Mother Jones, the redactions were applied only visually, and observers noticed that the text could be copied from underneath the black boxes. The hidden passages were then reported widely.
The lesson is not about one case. It is that a file can look redacted and still carry the text, and that anyone who can open the PDF can test for it. The American Bar Association's Judges' Journal has also published an article on embarrassing redaction failures if you want more cases.
What Can Still Leak After a "Redaction"
| Where it hides | How it leaks |
|---|---|
| Text under a box | Select, copy, paste, or search |
| Document properties (metadata) | Author, title and software are visible in file properties |
| Comments and attachments | Can hold the original wording or whole files |
| Hidden layers or form fields | Content that is not visible on the page but is still stored |
| Other copies | The original file, an earlier version, or a cloud backup |
What Proper Redaction Does
A proper redaction tool removes the underlying text and graphics from the file when the redaction is applied, and ideally clears hidden data and metadata too. Adobe's help pages say the same about Acrobat: redaction can permanently remove text and images, there is a separate option for removing hidden data and metadata in the Apply Redactions step, and the changes are not final until you save. Adobe also recommends saving under a new file name so you keep the original. See Adobe's page on removing sensitive content from PDFs for the steps in Acrobat.
There is another approach that does not need Acrobat: rebuild each page as a flat image with the boxes burned in, then make a new PDF from those images. There is no text item left to copy because the new file has no text layer. This is what our tool does.
How to Test Your Redacted PDF in Five Steps
Do this on the saved file, not on the editor window.
- Search. Open the file, press Ctrl+F (Cmd+F on Mac) and search for a word you redacted. There should be no matches.
- Select and paste. Select all text on a page (Ctrl+A), copy it and paste it into a plain text editor. The redacted words should not appear.
- Check properties. Open the document properties and look at author, title and subject.
- Try another viewer. Open the file in a second PDF viewer or in your browser, since viewers can differ in what they show.
- Read every page. Automatic find can miss spellings and details such as a name in a header or a number in a table. Look at each page yourself.
Tip: Some people suggest printing the page to a new PDF to flatten it. Whether that removes the text depends on the printer driver, so treat it as unproven until your file passes the search and copy test.
Redacting a PDF in Your Browser With TinyPNG Now
Our Redact PDF tool works like this:
- Open your PDF. It stays in your browser and is not uploaded.
- Draw boxes over what you want to hide, or use Find to mark every match of a word or a pattern such as an email, US phone number, SSN, card number or date.
- Choose the quality and download. Each page is rendered to an image with the boxes burned in, and a new PDF is built from those images.
- The tool then reopens the new file and reports how many text items it found, so you get a check without doing it by hand.
Limits you should know about
- The new PDF is made of images, so it is not searchable and the file can be bigger than the original.
- Find only works on PDFs that contain real text. For scanned pages, draw the boxes by hand.
- Automatic find can miss things, so check every page.
- The tool does not change your original file. Keep it in a safe place.
- This is not legal advice. Courts and agencies can have their own rules.
Before You Send: A Short Checklist
- Work on a copy and keep the original.
- Remove the content, do not cover it.
- Search and copy-paste test on the saved file.
- Check document properties.
- Read every page once more.
- Share the redacted file only, not the original and not an earlier draft.
Frequently Asked Questions
Is a black box enough to redact a PDF?
Usually not. A black rectangle drawn over text is a separate shape placed on top of the page. The text underneath often stays in the file, so it can still be selected, copied or found with search. Real redaction removes the text from the file.
How can I check that redacted text is really gone?
Open the saved file, press Ctrl+F (Cmd+F on Mac) and search for a word you redacted, then select all text on the page, copy it and paste it into a plain text editor. Also look at the document properties for author and title. If the word does not show up anywhere, the text is gone.
Does redaction also remove metadata?
Not always. Metadata such as author, title and software lives outside the page content, and some tools only remove it when you switch that option on. Adobe's help pages describe a separate option for removing hidden data and metadata when applying redactions. Check the document properties of the saved file.
Is printing a PDF to a new PDF a safe way to redact?
Not by itself. Depending on the printer driver, the new file can keep the text and the black box as separate items, so the text may still be selectable. If you use this method, test the result with search and copy and paste before sharing.
How does TinyPNG Now redact a PDF?
It draws the boxes in your browser, then renders every page to an image with the boxes burned in and builds a new PDF from those images. Because the new file contains no text layer, nothing is left under the boxes. The trade-off is that the new PDF is not searchable and can be larger.
Is this legal advice?
No. Courts, agencies and companies can have their own redaction rules. This guide explains how PDFs work technically. For filings or regulated documents, follow the rules that apply to you and have the final file reviewed.
Summary: A black box changes what you see, not what the file contains. Remove the text, clear the metadata, then test the saved file. You can do the first part in your browser with the free TinyPNG Now Redact PDF tool.
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Try the Redact PDF Tool →Sources
- Adobe: Removing sensitive content from PDFs
- Mother Jones: Paul Manafort failed redaction (January 2019)
- Nextgov: In wake of TSA breach, a refresher on redacting PDFs (2009)
- Redaction of PDF Files Using Adobe Acrobat Professional X (hosted by Columbia University)
- American Bar Association, Judges' Journal: Embarrassing redaction failures (2019)