Black out text in a PDF so it can't be copied

Drawing a black rectangle over text in a PDF editor often hides it only visually. The words are still in the file, and anyone can select them, copy them, or find them with search. To black out text for real, the text itself has to go. That is what Sumi does.

Why black boxes fail

A PDF stores text and drawings separately. A shape drawn on top covers the letters on screen but leaves them in the file. Highlighting text in black in a word processor and exporting to PDF has the same problem. Hidden metadata, such as the author or the original title, often travels along too.

What a real redaction removes

the visible text under each box;
the text layer of every page, so nothing can be selected or searched;
document metadata: title, author, creation dates;
attachments, links, scripts and form data from the original.

How to do it with Sumi

Drop your PDF into the app. It is processed in your browser.
Review the personal data Sumi found and switch each item to Remove or Keep.
To black out anything else, type it into "Redact a word or phrase everywhere", or use Draw box.
Preview shows the black boxes exactly as they will be exported.
Redact & download. Each page becomes an image with the ink painted into the pixels.

How to check the result in 10 seconds

Open the downloaded file and press Ctrl+A (or Cmd+A), then copy. Paste into a text editor: nothing comes out. Search for a word you removed: no match. Then open the document properties: no author, no title.

Limits

Because pages become images, the rest of the text can no longer be selected or searched either. Keep your original for your own records.

Questions

Is the result still readable?

Yes. It looks like the original, with black boxes where you chose.

Does this work for scanned PDFs?

Yes. Sumi reads scans on your device first, then redacts the same way.

Is my file uploaded?

No, the whole process runs in your browser.