How to redact a PDF properly (and why black boxes are not enough)

To redact a PDF properly, use a real redaction tool that removes the text and images underneath each black box, not just a drawing tool that covers them. Then test the result by searching for the hidden words and trying to copy them. If they cannot be found, the redaction worked.

Why black boxes are not enough

This is the most common redaction mistake, and it has caught out law firms, government departments and companies over the years.

When you draw a black rectangle or a thick highlight over text in a PDF, you add a new layer on top of the page. The original text is still there underneath. Anyone who receives the file can often:

• select the hidden area and copy the text into a message;
• search for a word and see it highlighted under the box;
• open the PDF in another app that does not show the box;
• move or delete the box, because it is just an annotation.

The page looks redacted, but the information has not gone anywhere.

What proper redaction means

Redaction is the permanent removal of information from a document, so it cannot be recovered from that file. A proper redaction tool does two things:

1. It deletes the text, images and drawings inside the area you mark.
2. It places a solid box where they were, so the reader can see something was removed.

After a true redaction, there is nothing under the box to copy, search or reveal.

How to redact a PDF properly on your phone

1. Make a copy of the original and keep it somewhere private.
2. Open the copy in a redaction tool.
3. Mark each piece of text or area you need to remove, such as account numbers, addresses or names.
4. Search for repeated details, like a reference number, and check every occurrence is marked.
5. Apply the redaction and save as a new file.
6. Test the result, as described below, before sending.

How to check a redaction worked

Never skip this step.

1. Open the redacted file, not the original.
2. Use search to look for a word or number you removed. It should find nothing.
3. Long-press inside a black box and try to select text. Nothing should select.
4. Open the file in a different PDF reader to make sure the boxes still appear and the text is gone.
5. Zoom in on the edges of each box for any letters that peek out.

Places where hidden data lives

Visible text is not the only thing that can give you away. Before sharing a sensitive PDF, think about:

• Metadata. The file's title, author and subject fields can contain names or project codes. See how to change a PDF's title and author.
• Comments and sticky notes that may contain notes you forgot about.
• Form fields with saved answers.
• Scanned pages, where the details are part of an image. A redaction tool should handle areas of an image as well as text.
• Headers and footers that repeat a name or number on every page.
• Bookmarks whose titles mention a person or case.

Redaction or flattening?

Flattening merges annotations and form fields into the page so they cannot be moved. It does not remove text that is hidden under a drawn box: it just fixes the box in place over it, and the text may still be copied. Redaction is the step that removes the information. You can flatten afterwards to lock in other edits. The flatten PDF guide explains the difference in more detail.

Common things to redact

• bank account and card numbers;
• national ID, passport and tax numbers;
• home addresses and phone numbers;
• names of children or third parties;
• salary figures in a document shared for another purpose;
• signatures, when only the content of the document is needed.

Redacting before using AI tools

If you want to ask an AI chatbot about a document, you may not want to share your personal details with it at all. Redaction removes them permanently. If you need the details back in the answer afterwards, a tool that hides and then restores them may suit you better. See how to hide your personal details before sending a PDF to ChatGPT.

Redacting with PDF Burrow

PDF Burrow has a Redact PDF tool that permanently blacks out sensitive text or areas, so the content underneath is truly removed rather than covered. The redaction runs on your phone, so the unredacted document is not uploaded. You can then tidy the file's title and author with Edit Metadata and check its details with PDF Info.

Frequently asked questions

Can I redact a PDF by highlighting it in black?

No. A black highlight is an annotation laid over the text. The words remain underneath and can usually be copied or searched.

Can redacted information be recovered?

Not from a properly redacted file, because the information has been deleted from it. It can be recovered from your original, so keep that copy private or delete it.

Should I redact a scanned document differently?

The process is the same, but the details are part of a picture. Make sure your tool removes the image area, not just text, and check the result carefully.

Does a password protect information as well as redaction?

No. A password keeps people out of the whole file. Anyone with the password still sees everything. Redaction removes specific details for everyone.