How to redact a PDF properly
By Dexaloop · Updated 27 October 2026 · Checked against the sources listed below
To redact a PDF properly, you must remove the sensitive text from the file itself, not just cover it. A black rectangle or highlight drawn over words only hides them from view; the text is often still there and can be copied out. True redaction deletes the content under each box (or turns the page into an image so no text remains), and then strips hidden data such as the title, author, comments and attachments. Always check the saved copy before you send it.
Why black boxes fail
A PDF page is built in layers. Text is stored as characters, and anything you draw, such as a black rectangle, is added on top. Your eyes see a solid bar, but a PDF reader still holds the characters underneath. Select the area, copy, paste into a text editor, and the words come back. Search often finds them too.
The same applies to other cover-up tricks. Changing the text color to black, placing an image over a paragraph, or shrinking the font to a dot all leave the characters in place. Anything a person can select, a program can extract.
This is not a theoretical risk. Two well-documented public cases show how it happens.
Real cases
The Manafort court filing, 2019
In January 2019, lawyers for Paul Manafort filed a court document with several passages blacked out. The Columbia Journalism Review reported that "Guardian reporter Jon Swaine noticed" the filing had not been redacted properly: "All he had to do was copy and paste some of the redacted text," and the hidden passages became readable.
The TSA screening manual, 2009
In December 2009, Nextgov reported that the US Transportation Security Administration "accidentally posted secret information detailing its airline screening practices." The manual had been published in redacted form, but copying the text into another program revealed the hidden sections. Nextgov put the cause plainly: "The information was exposed because of inadequate redaction procedures." The same article reminded agencies of the US National Security Agency's guide, "Redacting with Confidence," whose first tip is to "Delete, rather than black-out, sensitive text, diagrams, tables and images."
What true redaction does
There are two reliable methods.
| Method | How it works | Trade-off |
|---|---|---|
| Content removal | The tool deletes the characters, images or drawings inside each marked area and paints the box in their place | Rest of the page stays as searchable text; depends on the tool removing everything correctly |
| Page rasterizing | Each page with a box is turned into a picture with the boxes painted in, and the picture replaces the page | No text survives on that page at all; the page is no longer searchable and the file may grow |
Adobe Acrobat Pro uses the first method. Adobe's tutorial says that once you apply redactions, "the redactions and hidden information are permanently removed and saved to a new file," with a separate step to "remove information that is not visible in the file, such as comments, metadata, or hidden layers."
Don't forget the hidden data
Redacting the page is half the job. A PDF can also carry:
- Metadata: the document title, author name, and the software used. A title like "Draft settlement with J. Smith" can reveal as much as the text you blacked out.
- Comments and annotations: sticky notes and review remarks.
- Bookmarks: chapter titles in the sidebar can repeat a name.
- Attachments: files embedded inside the PDF.
- Form field values: data typed into fillable fields.
- Hidden layers: content switched off from view but still present.
Worked example: redacting a payslip
You need to send a 3-page bank application with a payslip on page 2. You want to hide your employee ID, your bank account number and your home address, and leave your name, employer and net pay visible.
- Mark 3 areas on page 2. Pages 1 and 3 have nothing to hide.
- Apply true redaction. If the tool rasterizes, only page 2 becomes an image. An A4 page drawn at 300 dpi is about 2,480 by 3,508 pixels, so expect that one page to add some size to the file.
- Clean the metadata. The file's title was "Payslip Sept - Employee 40213", which repeats the ID you just hid. Remove it.
- Test the copy. Search the saved file for "40213" and for your street name: 0 results on both. Select all on page 2, paste into a text editor: nothing from the hidden areas appears.
- Send only the redacted copy and keep the original somewhere safe.
Common mistakes
- Drawing shapes or using highlight in black. Annotation tools add a layer; they do not remove anything.
- Changing the text color to white or black. The characters are still there.
- Cropping the page. Cropping often only changes the visible area; the hidden part can remain in the file.
- Forgetting the same detail elsewhere. A name in the footer, a bookmark or the file name itself.
- Missing scanned content. Automatic search finds text, not handwriting, signatures or photos. Read every page.
- Sending the original by mistake. Name the new file clearly, for example "payslip-REDACTED.pdf."
Redacting in your browser
The Dexaloop Redact PDF tool does the work on your own device, so the file never leaves it. On any page where you place a box, it turns the page into a 300 dpi image, paints the box black and puts that image in place of the original page, which means the covered text is gone rather than hidden. Pages you leave alone pass through as they were. The title, author, bookmarks and attachments are stripped from the whole document. It pre-marks likely private details such as card numbers and IBANs, but it cannot spot everything: handwriting, signatures and names with no label still need a box from you, and scanned pages must be marked by hand. Go through every page before you save, and remember the original file is untouched, so keep it safe.
Redact a PDF in your browser: pdf.dexaloop.com/redact-pdf/. Free, no sign-up, and it runs on your device.
Questions
Is highlighting text in black the same as redacting it?
No. A black highlight or rectangle is an extra layer on top. The words underneath are still in the file and can usually be selected, copied or searched.
Does printing and scanning a document redact it?
Printing a page with black boxes and scanning it back produces an image with no hidden text, so it does remove the words. It is slow, lowers quality, and leaves the scan without searchable text. A proper redaction tool does the same job digitally.
What is PDF metadata and why remove it?
Metadata is information stored with the file rather than on the page, such as title, author and creation software. It can reveal who wrote the document or what it was called. Adobe groups metadata with comments and hidden layers as information that is not visible in the file.
How can I check a redaction worked?
Open the saved copy, select all text on the redacted page and paste it into a plain text editor, then search the file for a word you removed. Also check the document properties for title and author.
Can a redacted PDF be undone?
Not if it was redacted properly: the removed content is no longer in the file. That is why you keep the original separately and safe, and send only the redacted copy.
Sources
- Columbia Journalism Review: Manafort filing redaction (10 January 2019)
- Nextgov: In wake of TSA breach, a refresher on redacting PDFs (December 2009)
- Adobe Experience League: Remove sensitive information (Acrobat)
- Dexaloop Redact PDF tool page
This guide is general information, not legal, tax or financial advice. Rules change; check the official source for your own case. Found a mistake? Email support@dexaloop.com.