Redact a PDF so the hidden text is really gone

Why a black box is not enough

A PDF page is a stack of separate objects: lines of text, images, shapes. Drawing a black rectangle in an ordinary editor adds one more object on top. The text underneath is untouched, so anyone can select it, copy it, search for it, or simply delete the rectangle. Court filings, government reports and company documents have leaked this way many times, because on screen the covered version looks finished.

Real redaction removes the information from the file. This tool does that in the most dependable way available in a browser: every page you mark is drawn as a picture at the resolution you choose, the black boxes are painted into that picture, and the original page — its text layer, its images, its hidden objects — is left out of the new file entirely. What is under a box is not hidden. It no longer exists.

What happens to the rest of the document

Pages with no boxes are copied across exactly as they were, so their text stays sharp and searchable. The new file is built from scratch, which means the document's title, author, subject and keywords, its bookmarks and any attached files are not carried over. Those are places where a name or a reference number often hides without anyone noticing.

If you want to be certain that nothing at all survives — comments, links, form fields, hidden layers on unmarked pages — tick Rebuild every page as an image. The whole document then becomes pictures. It is larger and no longer searchable, but it carries nothing except what you can see.

Using search well

Search reads the document's text layer, which is how it can find a name on page 37 that you would have missed by eye. It has two limits worth knowing. It matches text within a single line, so a name split across two lines needs two searches or a hand-drawn box. And it cannot see text in a scanned page, because a scan has no text layer — only a picture of text. If search reports that the PDF has no text layer, mark the areas by hand.

The quick marks find email addresses, phone numbers and long runs of digits such as account, passport or card numbers. They are a starting point, not a guarantee. Always step through every page before you press the button.

Check before you send

1. Open the downloaded file and press Ctrl+F (or Cmd+F). Search for a word you removed. It should not be found.
2. Look at the edges of each box. A box that is a little too small can leave the tops of tall letters visible.
3. Look for repeats: the same number often appears again in a footer, a reference code or a barcode.
4. Rename the file if its name gives away what was removed.

For a fuller explanation of what goes wrong and why, read How to black out text in a PDF so it actually stays hidden.