Redacting a PDF on a Mac: Preview, Acrobat and alternatives

Why a black rectangle is not enough

A PDF keeps its text in a separate layer, even when a black shape covers it on screen. Drawing a rectangle, highlighting in black or adding an annotation only hides the content visually: the text is still in the file, selectable and copyable. Anyone can recover it with a simple copy and paste, or by extracting the PDF's text with a basic tool.

This is not a theory: the Manafort case, in 2019, remains the most cited example, detailed in our article on the black box on a PDF.

Properly redacting a PDF means deleting the text and images under the chosen area, not just covering them. That is what the tools described below do, to varying degrees.

Redacting with Preview on a Mac

Preview, the image and PDF viewer that ships with macOS, offers a redaction tool in the Tools › Redact menu in recent versions of macOS. The exact location may vary slightly with the system version, but the principle stays the same:

1. Duplicate the file to keep the original intact, then open the copy in Preview.
2. Go to the Tools menu and choose the redaction option.
3. Draw a rectangle over each passage to hide: name, address, number, whole paragraph.
4. Repeat on every page concerned.
5. Save and close the document: while it stays open, the redaction can still be changed; it becomes final when you close it.

The advantage: it is free, already installed, and works offline since the file never leaves your Mac. It is enough for occasional use: one or two documents, a few passages to hide.

The limits: the tool is manual, passage by passage. On a document of several dozen pages with many occurrences of the same name, it takes a long time and it is easy to miss one. Preview detects nothing automatically: it is up to you to spot every piece of sensitive information.

If the redaction tool is missing from your version of macOS, draw the rectangles, export each page as an image (JPEG or PNG), then rebuild a PDF from these images: the text becomes a non-selectable image, at the cost of search and copy in the document. A rectangle drawn and then simply exported or printed to PDF, on the other hand, leaves the text readable underneath.

Redacting with Adobe Acrobat Pro

Adobe Acrobat Pro offers a well-known redaction tool, with a search feature that can find every occurrence of a word or pattern (phone number, email address) in the document before marking them for deletion. This is useful on long documents where the same name comes up often.

The usual format: a Creative Cloud subscription with Acrobat Pro. On a Mac, processing happens in the installed application, so the file is not automatically sent to a server for the redaction itself. Cost and the subscription remain the main obstacle for occasional use.

Redacting with LibreOffice

LibreOffice, free and available on Mac, also has a real redaction tool: open the PDF in LibreOffice Draw, choose Tools → Redact, place the areas to hide, then use the redacted export offered by the redaction toolbar. The resulting PDF is made of images: no text left under the black areas, but a document that can no longer be searched or copied. Drawing simple black shapes and then exporting to PDF, however, leaves the text underneath.

If you still have the source file (Writer, Word), another approach is to replace the names and sensitive information directly in the text, then export again to PDF: the text no longer exists in the final PDF. Either way, the work remains manual: it is up to you to spot each passage.

AnonymFiles for redacting several files

These methods work well for a single document. For an entire case file, or for regular redaction, manual detection passage by passage becomes the bottleneck.

AnonymFiles is a desktop application, coming soon for Apple silicon Macs (M1 and later) and Windows, that processes an entire folder in one go, subfolders included: PDFs (text or scanned), Word (.docx), emails, spreadsheets, presentations, images, .txt and .md files. You drop the files in, the app automatically detects people, organizations, addresses, emails, phone numbers and IBANs, and replaces them with stable labels ([PERSONNE_1], [ORGANISATION_1]: the same person always gets the same label across the whole set). You compare the original and the anonymized copy side by side, you can redact by hand any passages the automatic detection missed, then export copies with neutral file names and an index of exported and excluded documents. In exported PDFs, the redacted text is actually removed, and metadata, annotations, forms and links are deleted.

Where Preview and Acrobat redact one file at a time, AnonymFiles is designed for the complete case file. On a Mac, no connection at all: the detection models are included in the application, which never connects to check a license, for telemetry or for a cloud AI chat (see the network scope on Mac). Your originals are never modified. Scanned PDFs and images are read by local OCR, and the pixels of the detected areas are erased in the image. And as with Preview, review the result before sending it.

Checking a redaction on a Mac

Whatever method you use, the check always follows the same logic:

1. Open the exported file, not the original.
2. Try to select the text under the blacked-out areas with the cursor.
3. Copy and paste the selection into a simple text editor (TextEdit, Notes) and see what appears.
4. Use the PDF viewer's search (Cmd+F in Preview) on a word you hid: if the search finds it, the text is still in the file.

This behavior, a rectangle that hides without deleting, is detailed in our article on the black box on a PDF that leaves the text readable. If you are unsure about what “redacting” actually means, our guide redacting a PDF step by step details the complete method, valid on Mac as well as Windows. Also think about metadata, which redaction does not always remove: see how to remove a PDF's metadata.

Which method to choose

For a single document and a few passages to hide, Preview is enough and costs nothing. As soon as the volume grows, when you need to process an entire case file or keep the replaced names consistent from one file to the next, local automatic detection such as AnonymFiles saves time without your documents leaving your Mac. In every case, a review is still needed before sending or publishing anything. For the complete process, see how to anonymize a PDF from start to finish.