Redact a PDF without uploading it anywhere

You can redact a PDF without uploading it by using PDF, the free PDF app in Madosuite, which runs in your browser on your own computer. The file never leaves your device, and redaction and sanitizing are among the features its developers list as good today.

The documents people redact are usually the ones they least want to send to a website: contracts, medical letters, bank statements, ID scans. That is the whole reason to do it locally.

Redaction removes text, it doesn’t cover it

A black box drawn over a line of text is not a redaction. The text is still in the file underneath. Anyone can select it, copy it, or search for it.

Real redaction deletes the content under the marked area from the file. Sanitizing goes further and cleans out hidden material a document can carry along. So a proper redaction has three parts: mark what should go, apply the redaction so it is removed, then sanitize and check.

Open the PDF

1. Go to the Madosuite desktop. No account is needed.
2. Open Files, press Upload and pick your PDF.
3. Open the file with PDF.

Upload here means copying the file into the home folder of the Linux machine that Madosuite runs in your browser. Nothing is sent to us. If the PDF has a password, PDF opens encrypted files too.

Mark, apply and sanitize

The quickest way to reach the tools is the command palette: press Cmd-K and type “redact”. You can also browse the All tools catalogue, which lists every tool in the app.

1. Find every occurrence first. Use search, which finds matches as you type. Note every page where the name, number or address appears.
2. Mark the areas you want removed with the redaction tool. Cover the whole word or line, not just part of it.
3. Apply the redactions. Marking only shows what will go. Applying is the step that removes it.
4. Sanitize the document. Use the sanitize tool on the redacted file.
5. Check the document properties. Document Properties shows the title, author, subject and keywords, which you can edit. A title or author field can give away exactly what you redacted.
6. Save as a new file. See the next section for why.

Save to a new file, not over the original

PDF saves in two ways. An incremental save appends your changes to the end of the file and leaves the original bytes untouched. That is a good thing for ordinary edits, because nothing is lost. For redaction it is the wrong thing to rely on: you want a file where the removed text is gone, not one where the old version is still inside.

So save the redacted document as a new PDF with a new name, and keep the unredacted original somewhere private. Then open Files and download the new file.

Check that it worked

Don’t send the file until you have tested it.

1. Open the new, saved file in PDF. Open the saved copy, not the one you were editing.
2. Search for each word or number you removed. Search should find nothing.
3. Try to select text in the blacked-out areas. Nothing should be selected.
4. Look at the bookmarks and attachments. Both can hold text that is not on the pages.
5. Check Document Properties once more.

If search still finds a match, go back to the original, redact again, and save a new copy.

Limits

• PDF is alpha. That is the app’s own status. Redaction and sanitizing are listed as good today, but test every file as above.
• Scanned pages. If a page is a scanned image, the words are pixels, not text, so search cannot find them. Check scanned pages by eye. OCR beyond Latin script is listed as thin or missing.
• Editing existing text is not reliable yet, especially CJK and right-to-left text. Redact; don’t try to rewrite the sentence.
• No printing from the browser. The web build of the app cannot print, so download the file and print it elsewhere if you need paper.
• Hostile files. The developers say fuzzing still finds crashes and hangs on deliberately broken files.
• Clearing the site’s data in your browser deletes the files in Madosuite’s home folder. Download what you need to keep.

PDF is one of the ArtCraft team’s open-source Crafting Apps (MIT or Apache-2.0), shipped in Madosuite under the name PDF.

For the short version of these steps, see the redact a PDF tool page, or read what “no upload” really means. Everything else the app does is on the PDF app page.