How do I black out text in a PDF?

Last reviewed: October 21, 2026 · Markdown version

Use a redaction tool, not a black shape. A rectangle or a pen stroke drawn over a word is a mark laid on top of the page, and the word is still in the file underneath it. Adobe Acrobat and Apple's Preview on a Mac both have a tool that removes the text itself; the phone apps we checked, Preview on iPhone and Files by Google, document marking tools but no redaction. Below are the steps for each, and a two-minute check to run before you send the file to anyone.

Why a black box is not enough

Apple's Preview guide shows how loose a drawn mark is. Annotations stay editable unless you go out of your way: "To save a PDF and allow annotations to be edited later, choose one of the following: File > Save, File > Export, or File > Export to PDF" (Annotate a PDF in Preview on Mac, Preview User Guide, read 21 October 2026). A box someone can edit is a box someone can move. On Android, Files by Google puts a "Hide annotations" control in its PDF editor (Open, manage & edit PDFs in Files by Google, Files by Google Help, read 21 October 2026), so a reader with the same app can switch your pen strokes off. Neither page says what text sits under a mark, but the Preview page itself separates the two jobs: its tool list has Shapes and Draw for marking, and a different tool, Redaction Selection, for removing text.

Adobe Acrobat: the Redact a PDF tool

Adobe's steps: select All tools > Redact a PDF, choose Redact text and images, drag over the text or picture, then select Apply. Acrobat then asks whether to sanitize and remove hidden information, and saves the result as a new file through a Save Sanitized Document dialog (Redact sensitive content in Acrobat Pro, Acrobat Desktop Help, read 21 October 2026). When one name or number appears many times, Find text and redact searches for it as a "Single word or phrase", "Multiple words or phrase" or "Patterns", and Check All marks every occurrence at once (Search and redact text in Acrobat Pro, Acrobat Desktop Help, read 21 October 2026). Adobe's redaction pages are titled for Acrobat Pro, so expect to need that edition rather than the free Reader.

Adobe states two limits plainly. "Redaction is permanent and cannot be undone once applied and saved", so keep the original somewhere safe. And "Redaction removes only visible text and graphics. Hidden data, such as metadata or embedded content, must be sanitized separately" (About redacting and sanitizing PDFs in Acrobat Pro, Acrobat Desktop Help, read 21 October 2026). That second line is why the sanitize toggle matters: a name can survive in a file's properties after it has gone from every page.

Preview on a Mac: Redaction Selection

Apple's Markup toolbar includes a tool described as "Select text to remove it from view. You can change the redaction as you edit, but once you close the document, the redaction becomes permanent." Apple adds one caveat worth reading twice: "If the PDF has a table of contents, entries in it that link to redacted text aren’t removed" (the Annotate a PDF in Preview on Mac page above). If your file has a bookmarks sidebar, look through it after redacting.

On a phone

We found no documented redaction tool in the two phone apps whose help we read. Apple's Preview on iPhone lists copying, highlighting, underlining and striking through text, plus "stickers, signatures, shapes, or text" (Annotate a PDF or image in Preview on iPhone, iPhone User Guide, read 21 October 2026). Files by Google offers a pen, a highlighter and an eraser (the Files by Google page above). Every one of those adds a mark; none of them is described as removing text. Our advice for anything sensitive is to redact on a computer with one of the tools above.

Check it before you send it

This is our own routine, not a vendor's. Open the saved copy, not the one you edited, and search it for the exact word you removed. If the find bar still lands on it, the text is still there. Then try to select the blacked-out area; if words highlight underneath, the redaction did not take. Searching for a word in a PDF has the find steps for each app.

When the redacted copies are a batch rather than one file, DocFind on iPhone or Android can run that check across all of them at once: it searches inside many PDFs and shows the file, the page and the surrounding text for every hit, so a name that should have gone shows up with its page. It does not edit, annotate or sign PDFs and never changes the files you search, so it cannot do the redacting itself. It searches PDFs only, and its search covers the page text; Adobe's sanitize step is still how you clear a file's hidden data.