How to Hide Personal Information in a PDF Before Sharing

You need to send a bank statement, a rental agreement or an ID form, but parts of it are not for the other person. An account number here, a home address there. The obvious fix is to draw a black box over those parts. That fix often fails, and this guide explains why and how to do it properly.

Why a black rectangle is often not enough

Many apps let you place a black shape on top of a PDF page. It looks right on the screen, but the words are still stored in the file, right under the shape. Anyone can select the text, copy it, or move the rectangle away. News stories about leaked documents have started this way more than once.

Real redaction means the hidden content is removed from the file. Nothing is left under the box.

How to tell a real redaction from a black box on top

A black box drawn on top of a page is only a picture lying over the words. You can test any file in a minute:

• Tap and drag across the black box. If you can select words, the text is still there.
• Search the file for a word you hid. If the viewer finds it, it is not removed.
• Copy the page text and paste it into a notes app. If the hidden words appear, anyone can read them.

A real redaction fails all three tests, because nothing is left under the box. Run these tests on every file you share.

What you need

• The PDF on your phone or computer
• A list of the details that must not be shared
• A few minutes to check the result

Step 1: Open the Redact PDF tool

Open our Redact PDF tool, tap the box and choose your file. It stays on your device. It is not uploaded, which matters a lot when the file holds exactly the details you are trying to protect.

Step 2: Let the tool find the words

If the PDF has real text, type the words to hide into Words or numbers to mark. Use a comma between several, for example a name, an ID number and a phone number. Then tap Find and mark. Every match gets a black box, and the tool tells you how many it marked and on how many pages.

This does not work on a scan or a photo of a paper, because those pages hold a picture and no text to search. The tool says so when it finds no text. Then you draw the boxes yourself.

Step 3: Draw boxes by hand

On a computer, drag with the mouse over anything else you want to hide. On a phone, scrolling and drawing compete for your finger, so there is a button that switches between them. Turn drawing on, drag over the details, then switch back to scrolling to move to the next page.

• Tap a box to select it, then use the red cross to remove it.
• Undo last box and Remove all boxes help if you lose track.
• Make boxes a little larger than the details. A box that leaves a sliver of a letter showing hides nothing.

Step 4: Save and check

Choose a picture quality if you need to. Standard is fine for most pages, and Sharp helps with small print. Tap Save redacted PDF.

What happens inside: every page with a box becomes a picture of the page with the boxes painted on, and the original page is not kept. Pages without boxes are left as they are. Hidden document details, such as the title, author and keywords, are removed, and so are bookmarks, comments and form data.

Because marked pages are pictures, you cannot select or search their text any more. That is the price of making the removal real.

Step 5: Check it like a stranger would

Do not trust, check. Before you send the file:

1. Open the saved PDF and look at every page, not only the first.
2. Try to select text under a box. Nothing should be there.
3. Search the file for a word you hid. It should find nothing on the marked pages.
4. Look at the file details in your PDF reader. The title and author should be empty.

Other things to remember

Information can hide in places that are easy to forget: a name in a page header, a signature, a barcode, a file name. If a file must be locked as well, add a password with Protect PDF, and send the password in a different message. Cutting off the edge of a page with Crop PDF only hides it, so never use cropping for private details.

A note on privacy

Everything happens in your browser. The PDF, the pictures of its pages and the finished file never leave your device. When you close the tab, they are gone.