A tenancy agreement for a council application with your bank details on it. A medical letter for an employer that only needs one paragraph. A screenshot-heavy report going to a client, with a colleague’s phone number in it. Before a PDF like that goes out, something has to be blacked out, and Adobe’s Redact tool, the one most guides point to, is only in the paid Acrobat Pro, Premium and Studio plans, not in the free Reader or in Acrobat Standard.
The free ways that come to mind first, drawing a black box or highlighting in black, have a catch that has embarrassed law firms and governments for years: the text is still in the file. So this guide starts with what goes wrong, then the ways that actually work, then how to check a redacted PDF yourself in under a minute.
Why a black box is not enough
A PDF keeps its text and the things drawn on top of it separately. A black rectangle covers the words on screen and on paper, but the words themselves are still there, and anyone can select the area, copy it and paste it into a text editor. We tried six ways of blacking something out that people commonly use, and then read each file back with an ordinary PDF text extractor (pypdf):
| How it was blacked out | Hidden text read back? |
|---|---|
| Black shape placed over a name in a document, then saved as PDF (Chrome’s Save as PDF) | Yes: “Maria Gonzalez” |
| Text coloured black on a black background, saved as PDF | Yes: “QQ 12 34 56 C” |
| Black background behind the text (a black highlight in a word processor), saved as PDF | Yes: “07700 900123” |
| Black rectangle drawn on the PDF page with a shape tool | Yes: “11112222” |
| Black filled box added as a comment (rectangle annotation) | Yes: “33334444” |
| PDF highlighter set to black | Yes: “55556666” |
Six out of six. Every one of them looked properly redacted on screen. There is a second leak that none of these touch: the document’s properties. Our test case file showed “Jane Doe” nowhere on page 3, yet its title was “Case file - Jane Doe” and its author “Jane Doe”, and Chrome shows the title in the tab.
Way 1: free, in the browser (Windows, Mac, Chromebook, phone)
Our Redact PDF tool does real redaction without uploading the file:
- Open the page and drop the PDF.
- Type the names, numbers or words to remove, one per line. Tick All email addresses or All phone numbers if you need them, and press Find on every page. Every match on every page gets a black box, including ones in capitals or on a rotated page.
- Page through and drag a box over anything else: a signature, a photo, a stamp, a scanned paragraph. Click a box to remove it.
- Press Redact and save.
Each page with a box is redrawn as an image with the box painted into it, so there is no text left under the box at all; pages without boxes stay as they were, with selectable text and working links. The title, author, bookmarks, comments and form fields are left out of the copy. Then the tool searches the saved file again and lists what it found. In our test with a three-page case file, it found the name five times, an email, a phone number and an account number; in the saved file a separate extractor found none of them, not even in the raw bytes, and when we drew the pages with a different PDF engine, every redacted word was fully black and the words next to them were still readable.
Way 2: Preview on a Mac
Preview has its own redaction tool. Apple’s Preview guide describes it: click the Markup button, choose the Redact tool (a rectangle with a line through it, called Redaction Selection) and select the text to remove. Apple notes three things worth knowing: make a duplicate first, because the redaction becomes permanent once you close the document; redactions can be adjusted only until then; and table of contents entries that link to redacted text are not removed. Check the document properties as well (Tools > Show Inspector).
We could not test Preview ourselves, so use the checks below on the result, as with any tool.
Way 3: Adobe Acrobat Pro
If you already pay for Acrobat Pro, its Redact tool marks text, search results or whole pages and then applies them. Adobe’s own help is careful to say that redaction removes visible text and graphics, and that hidden information such as metadata, comments and attachments needs the separate Sanitize step. Do both. The free Acrobat Reader and Acrobat Standard cannot redact.
What does not work, even though it looks right
- Drawing a box or highlighting in black with a PDF viewer’s drawing or comment tools: we tried a drawn rectangle, a box comment and a black highlight, and the text stayed under all three.
- Covering text in a document and exporting it to PDF: a shape over text is still a shape over text in the PDF. In our test, a page saved as PDF from Chrome gave the covered name straight back.
- Printing to PDF (Microsoft Print to PDF, Save as PDF): it usually keeps text as text, so whatever was under a box comes along.
- White boxes and white text: the same problem, only harder to notice.
Printing on paper and scanning does work, because the result is only a picture of the page, but it also turns every page into an image and needs a scanner.
Check a redacted PDF in under a minute
- Open the redacted file, press Ctrl+A (Cmd+A on a Mac), copy, and paste into Notepad or TextEdit. If a hidden name appears, it is not redacted.
- Press Ctrl+F in the PDF viewer and search for each hidden word.
- Look at the document properties: in Chrome’s PDF viewer, the ⋮ menu has Document properties; in Acrobat Reader, File > Properties. The title and author should not name anyone you redacted.
- Or drop the file into Extract Text from PDF: what it shows is exactly what anyone can copy out of it.
Quick answers
How do I black out text in a PDF without Adobe Pro? Use a redaction tool that removes the text, such as Redact PDF in the browser or Preview’s Redact tool on a Mac. A black box or a black highlight in a free PDF viewer only covers it.
Can a redacted PDF be un-redacted? A real redaction cannot: the text is gone from the file. A fake one can be “un-redacted” by copying, or by deleting the box in any PDF editor.
What if the whole page is sensitive? Leave it out instead: Delete PDF Pages builds a new file without those pages, so they are not hidden in it either.
Does redaction work on a scanned PDF? Yes, but searching cannot find words in a scan, because they are part of a picture. Draw the boxes by hand and check every page.