How to redact a PDF so the text is really gone
Real redaction removes the text and image data under the marked area from the file, so no reader, search or copy can bring it back. A black rectangle drawn in an editor only covers it, and the words are still one select-all away. Use a redaction tool, then test the result by trying to copy the hidden text and by searching for it.
Redact PDF removes the content under each box rather than painting over it. The file is processed on our server and deleted within 24 hours, as the tool page states. Redact PDF
Redacting a document, step by step
- Make a copy of the original and work on the copy. Redaction is permanent by design.
- Mark every occurrence of each item, not just the first one. Names repeat in headers, footers and signatures.
- Apply the redaction and download the new file.
- Open the result and try to select the text where a box is. If anything highlights, the redaction did not take.
- Search the file for a word you removed. A real redaction returns nothing.
- Check the document properties for the author, title and subject, and remove anything you would not want seen.
Why a black rectangle is not redaction
A PDF is layers of instructions: draw this text here, draw this shape there. A rectangle added in an editor is one more instruction, placed after the text, so it is painted on top. The text instruction is still in the file. Anyone can select through the box, copy the words out, or simply delete the rectangle in another editor. Court filings, freedom of information releases and job applications have all leaked this way, and the leak is usually discovered by a stranger.
What proper redaction removes
A redaction tool deletes the text runs under the marked area, cuts the pixels out of any image beneath it, and removes annotations and form field values that overlap it. It then draws the box so the reader can see where something was. The file is rewritten, so the removed content does not survive in an older version inside the same file, which is a trick plain editors fall for.
Metadata and hidden text
The words on the page are not the only words in the file. The document properties can carry an author name, a company and an original title. Bookmarks name the sections. A scanned document that was made searchable carries an invisible text layer with every word the recognition found, including the ones you just blacked out on the image. Check the properties, and if the file came from a scanner with recognition, sanitise it or redact the text layer as well.
Checking your work
Three tests catch nearly everything. Select all on each redacted page and look for highlights inside the boxes. Search for two or three of the removed words. Copy the whole page into a plain text editor and read what arrives. If all three come back clean, the redaction held. Do the tests on the downloaded file, not on the preview, because the preview is the editor’s view, and the file is what you will send.
Strip scripts and embedded files as well
Scanned documents are different
A scan is a picture, so a box drawn over it and then flattened genuinely hides the pixels beneath, provided the box is opaque and the result is re-saved as a flat image. The danger with scans is the recognition layer described above and the original image left inside the file by a lazy editor. A redaction tool handles both; a paint program does not.
Questions people ask next
Can I just convert the redacted PDF to an image to be safe?
Converting the page to a flat image and back does remove hidden text, at the cost of making the document unsearchable and larger. It is a reasonable last step after redaction, not a substitute for it, because the metadata survives the round trip.
Does highlighting in black in a PDF viewer count as redaction?
No. A highlight is an annotation drawn on top of the text, and the text remains selectable underneath it. Some viewers even let the next reader change the highlight colour and reveal the words.
Is the redacted file private?
Redact PDF processes the file on our server because the rewriting cannot be done reliably in a browser. The tool page explains this, and files are deleted within 24 hours. If the document is too sensitive to leave your device, flatten a black box over a scan instead and accept the limits described above.