How to Redact a PDF Properly (Not Just Cover It Up)

Failed redaction has exposed witness names, unredacted settlement figures and classified passages in court filings, and it happens the same way every time: someone drew a black rectangle over the text and saved the file.

Why a black box is not redaction

A PDF page is a stack of drawing instructions. Adding a filled rectangle adds one more instruction on top. The text instruction underneath is untouched — it is simply covered, the way a sheet of paper over a screen covers what is displayed.

Select the area and copy it, and the clipboard contains the words. Extract the text and they are all there. Delete the rectangle and the page reads normally again.

What real redaction does

Proper redaction removes the underlying content rather than hiding it. The text instructions inside the marked area are deleted and the region is filled, so there is nothing left to recover — no copy-paste, no extraction, no undo.

Slate PDF takes the bluntest route to that guarantee. Every page you redact is redrawn as an image with the black boxes burned into it, and the original page — text, fonts and all — is thrown away. Pages you did not touch are copied across unchanged, with their text still selectable.

How to redact a PDF online, free and without uploading

There are two routes, depending on how much of the page has to go. Both run in your browser, so the document never leaves your device, and neither needs an account.

Black out specific passages

1. 1Open the PDF Workspace, add your document and switch to the Redact tab.
2. 2Drag a box over each passage that must be removed, moving page by page through the preview.
3. 3Cover the whole passage, and the whole field rather than just the digits — partial redaction leaves fragments that are often enough to reconstruct the rest.
4. 4Apply the redaction and download the result.
5. 5Verify: copy from the redacted areas and confirm nothing comes back.

Black out entire pages

1. 1Open the Redact PDF tool and add your document.
2. 2Click the thumbnail of every page that must be blacked out.
3. 3Run the redaction. Each selected page is replaced by a solid black page; the rest are left as they were.
4. 4Download the result and check the page count still matches the original.

When redaction matters

• A school report or reference letter that names a child, a diagnosis or personal history.
• A contract shared with a third party, where pricing, account numbers or addresses must stay private.
• A claim, receipt or statement whose bank details have to go before it is filed or forwarded.
• Disclosure bundles and subject access requests, where third parties' names must be removed.

What people forget to redact

• The same name appearing in a header or footer on every page.
• Document metadata — author, title and subject fields often name the person.
• Bookmarks and the outline, which can restate a redacted heading.
• File attachments embedded in the PDF.
• Comments and annotations left by reviewers.
• A filename that gives away exactly what you redacted inside.

Metadata is invisible in the reader and trivially readable by anyone who looks. Slate PDF builds the redacted file as a new document, so the original title and author fields are not copied across — but open the document properties on the result anyway, and strip anything left as a separate step.

Redacting scans, signatures and images

A scanned page has no text objects to remove, so the box itself destroys the information: the marked pixels are painted black in the new image. The same goes for a handwritten signature, a stamp, a photo or a logo — anything you can draw a box around is gone from the output.

If the document has been through OCR, it also carries an invisible text layer that still contains the words. On a page Slate PDF redacts, that layer is discarded along with everything else. Pages you did not redact keep theirs, so search the whole file for the removed name before you send it.

Before you send it

1. 1Copy from every redacted area and confirm nothing is returned.
2. 2Search the document for the name or number you removed.
3. 3Check the metadata.
4. 4Check headers, footers and bookmarks.
5. 5Have a second person look, if the stakes justify it.