How to redact a PDF properly (so the text is actually gone)

You can now redact a PDF on reader.me: Redact a PDF. Mark what should not be read with your mouse or finger, download the file, done. The interesting part is what happens underneath, because that is exactly where most homemade methods fail.

The underlying problem

Draw a black rectangle over some text in any editor and the text is still there. Still in the file, still selectable, still recoverable in two minutes. The rectangle is a layer painted on top, not an eraser. This article covers real cases where that has gone badly wrong.

For redaction to be real, the content has to stop existing — not get covered up.

How the tool works

When you mark an area and hit Redact:

1. The page you marked is drawn as an image, with the black areas already painted on it.
2. That image replaces the original page in the new PDF.
3. The original page, with its text, is gone from the file. Not underneath: gone.

You can verify it yourself with the extract text tool: run the redacted PDF through it and what you covered will not come back.

The cost, stated plainly

Turning a page into an image has consequences, and I would rather tell you now than after:

• The redacted page loses selectable text. You cannot search inside it or copy and paste from it. It reads perfectly well, but it is an image.
• It gets heavier. A page of text is a few kilobytes; as an image, a few hundred.
• Pages you do not mark are copied untouched. A 40-page contract with one redacted area keeps 39 pages of normal text. Only what you touch is converted.

It is a deliberate trade: convenience for safety. On a document you are about to send with sensitive data in it, safety wins.

What it does not cover

The tool removes what sits under the boxes, and it also clears the metadata of the resulting document — author, software, dates. What it cannot do is guess. If the name you want hidden appears five times and you cover one, the other four are still there. Go through the whole file before sending it, page by page.

And one piece of common sense: always keep the unredacted original somewhere safe. There is no undo for this, which is rather the point.

It happens in your browser

A document that needs redacting is, by definition, a document you do not want to upload anywhere. Uploading it to a website in order to censor it is a fairly large contradiction, so that is not what happens here: the file is processed on your machine and never reaches a server. You can disconnect before dropping it in and the tool will still work.

Redact a PDF