When you need to share a PDF document—such as a bank statement, a legal contract, or a medical record—with a third party, you must ensure that highly sensitive information (like your Social Security number or personal address) is completely unreadable. Simply drawing a black rectangle over the text using standard markup tools is incredibly dangerous; anyone with basic computer knowledge can easily delete the rectangle or copy the hidden text underneath it. To securely and permanently destroy the underlying data, you must use the Redact tool built directly into the macOS Preview app.
How the Redact Tool Works
Unlike standard drawing shapes that simply sit on top of the text as an overlay layer, Preview’s Redact tool physically alters the core structure of the PDF file. When you redact a sentence, the tool permanently deletes the actual text data from the file’s code and replaces it with a solid black bar. Once the file is saved and closed, it is mathematically impossible to recover or copy the hidden text.
How to Securely Redact Information
The Redact tool is located inside the advanced markup menu.
- Double-click your PDF to open it in Preview.
- Click the Markup Toolbar icon in the top right corner of the window (the circle with a pencil tip inside).
- In the newly revealed toolbar, look to the far left side and click the Redact icon (it looks like a small black square with a white line through it).
- A severe warning popup will immediately appear on your screen, explaining that redaction permanently removes the content from the document. Click OK to accept the warning.
Your mouse cursor will change to a crosshair. Navigate to the sensitive information in your document (e.g., your bank account number).
- Click and hold your mouse button, then drag the cursor completely over the sensitive text to highlight it.
- Release the mouse button. The text will instantly be replaced by an impenetrable black box with an ‘X’ pattern across it.
You can repeat this process for any other sensitive paragraphs or images in the document.
Crucial Final Step: The redaction is not permanent until you save the file. If you make a mistake, you can still press Command + Z to undo it. Once you are absolutely certain the redactions are correct, press Command + S to save the document. The hidden data is now permanently destroyed, and the file is safe to email to third parties.