Black out details in a PDF so they can't be copied

The short answer: picture first, then cover, then PDF

Say you want to send a bank statement, a salary slip or an ID copy, but hide an account number or an address. If you draw a box over the PDF itself, the words may still be there underneath. If you cover the words on a picture of the page, they are gone, because a picture holds only dots, not letters. The routine has five steps:

1. Turn the page into a PNG with PDF to PNG, at Normal sharpness.
2. Cover the details on the PNG in your photo app, with a solid dark box.
3. Save it as a new PNG, with the box flattened into the picture.
4. Make a PDF from the new PNG with PNG to PDF.
5. Check it: open the new PDF and search for the hidden words. They should not be found.

Both tools run inside your browser, so the unhidden version of your page is never sent anywhere while you do this. The rest of this post explains why a box on top isn't enough, how to check, and how to do each step well.

Why a box drawn on a PDF may not hide anything

A typed PDF, such as a statement from a bank, stores its words as real text. Anything you draw on it, whether a black rectangle, a highlighter or a white patch, is a separate layer sitting on top. The words below are still part of the page. Depending on the program that made the box, someone may be able to:

• Select and copy the words from underneath the box, then paste them into a message.
• Search for a number and find it, even though it looks hidden.
• Move or delete the box in some PDF programs, and see what was under it.

This is a well-known way that private details leak out of "hidden" documents. It isn't about your tool being bad. A box is a drawing, and the text is still in the file.

A picture is different. When a page is turned into a PNG, the letters become coloured dots. A black box on those dots replaces the dots that were there, and nothing is left to select, search or move. That is the trick this post uses. The cost is that the final PDF is pictures only, which the table in the "What changes" section shows.

First, see if the details are still there

You can test any PDF in a minute, yours or the one you got back from someone else. Open it in the PDF viewer and:

1. Press the magnifier, or Ctrl+F, and type a word or number that is meant to be hidden.
2. If the viewer finds it and marks it in yellow, the words are still in the file, even if a box covers them.
3. Try to select the line with your mouse, or press and hold a word on a phone. If it highlights, it can be copied.

The viewer's search ignores capital letters and accents, and finds a phrase even if it breaks across two lines, so it is a fair test. It finds nothing in a scan or a picture, and says "No text". That is what you want to see after the routine in this post. Reading and searching happen on your device; the viewer never sends your file anywhere.

One more case: if your PDF is already a scan, its pages are pictures, and a box drawn in a picture editor is safe. You would still do the same steps, but the file size may behave differently (see the size section).

The routine, step by step

1. Turn the page into a PNG

Open PDF to PNG, choose your PDF and leave the format on PNG. Use Choose pages to type only the page numbers that need hiding, like 1. Pick Normal (150 ppi). An A4 page then becomes a picture of 1240 × 1754 pixels, sharp enough for text and numbers to be read on a phone or a laptop. Use High (2480 × 3508 pixels) only if the page has very small print. Press Convert. Pictures of a single page come with their own Download button, and no ZIP.

2. Cover the details

Open the PNG in your gallery or photo editor and find its markup or drawing tool. Our tools do not edit pictures, so this part happens in your own app. Draw a solid, dark box over each detail:

• Use a solid colour at full strength. A highlighter, a faint pen or a see-through box lets the shape of the letters show.
• Make the box a little bigger than the text, so no edge of a letter peeks out.
• Avoid blur and pixelate. They may leave enough of the digits' shape for someone to guess the number.
• Cover every place the detail appears: the header, the table, the footer and any stamp or barcode that carries it.

3. Save a flattened copy

Export or save the edited picture as a new PNG, not as the editor's own project file. A PNG has only one layer, so the box becomes part of the picture. Keep your original PDF and PNG somewhere private, or delete them when you are done.

4. Make a PDF from the PNG

Open PNG to PDF and add the edited PNG. For a page that was A4 to start with, pick A4 and leave the margin on None, since the picture already has the paper's white edge. Press Convert. A plain PNG goes in exactly as it is, so the box and everything else stay as you saved them. Our guide shows this: a 70 KB PNG form made a 71 KB PDF.

5. Check the result

Open the PDF in the PDF viewer. Zoom in on every hidden place, then search for a hidden word. You should see "No text", and nothing should be selectable.

What changes when a page becomes a picture

This routine gives up some things in exchange for real hiding. Know them before you start:

• No search, no copying. The text is now part of the picture. You can read it, but you can't search or copy it. For a document going to a human reader, that is usually fine.
• No links or form fields. They don't work in a picture.
• A bigger file. A typed page is tiny, and a picture of it is larger.

Here are the sizes from our tests, as shown on the tool pages:

A PDF made of plain PNGs is about as big as the PNGs themselves. So choose Normal over High, and do only the pages that need hiding. If the final file has a size limit, Resize PDF will bring it under that limit. Quality may drop to reach a small size, so check the covered places afterwards.

If your PDF is a scan, its pages are pictures already. For those, JPG is smaller than PNG: page 1 of our sample scan was 2.85 MB as a PNG and 422 KB as a JPG at Normal, with no visible difference. Use PDF to JPG for the page, cover the details, and convert back with JPG to PDF.

Only one page needs hiding? Keep the rest as they are

A statement or a bundle often has one page with private details and several that are fine. You don't have to turn the whole file into pictures. Put the picture page in place of the original:

1. Do the routine above for the one page, and make a one-page PDF of it.
2. Open the full PDF in Organize PDF and press Add pages from more PDFs to bring in the new page.
3. Drag the new page into place and delete the original page. The post How to replace a page in a PDF has the details.

Pages that were not changed keep their text, their links and their quality, because Organize PDF copies pages as they are. The added page is pictures only. Delete the original page, and check the result with the viewer's search, which should still find words on the untouched pages, but not the hidden words.

What to hide, and what to leave visible

Hiding helps only if the person receiving the file doesn't need the hidden detail. A bank, a government form or a verification may need it complete, and then a covered number makes the file useless. Ask what is needed, and the receiver's notice always wins.

These are common cases, not rules. Some government portals can also give you a version of a document with part of a number already hidden. If yours does, using that is better than hiding it yourself. For an ID copy you will send to several places, stamping the purpose across the copy is a good second step.

Common mistakes, and how to avoid them

Sending the original along with the new file.

The picture PDF is safe, but the original is not. Check which file you attach, and give the new one a clear name such as statement-hidden.pdf.

Covering with a highlighter or a light colour.

The shape of the letters can show through. Use a solid, dark colour at full strength.

Missing a second place.

A number often appears in the header and the table. Zoom in and read the whole page once more before you save.

Saving with layers.

If your photo app lets you save a project, keep that for yourself. For the file you send, export a plain PNG.

Forgetting the file name.

A name like aadhaar-1234-5678-9012.pdf shows what you hid. Rename the file before sending.

Sending it by chat as a photo.

Chat apps may make a picture smaller and softer. For a PDF, send it as a document.

The page you are hiding never goes online

It would defeat the point to upload a page full of private details to a website so it can be hidden. These tools have no upload step and never send your files anywhere: your own browser draws the page and builds the PDF. The page contacts only this site and Google's ad service, which shows the ads that keep the tools free, and our code never gives your files to the ad code. The privacy policy has the details.