How to properly hide information in a PDF
The mistake behind the famous leaks
In every well-known case the pattern is identical: someone opened the document, drew filled rectangles over the sensitive lines, exported, and sent it. The recipient selected the page, pressed copy, and pasted the hidden text into a note. The rectangle is a graphic; the text layer sits beneath it, untouched.
Screenshotting the page and rebuilding the PDF from the image does technically work, because it throws away the text layer entirely — but it also makes the document unsearchable and much larger. It is a workaround, not a method.
What else can identify a document
Redacting the visible text is not always enough. A PDF can carry the author's name, the original file path, the software used, and in some workflows earlier revisions of the page. If you are sending a document to someone who should not know where it came from, check the document properties as well.
When in doubt
If a document is genuinely sensitive — medical, legal, financial — verify with the search test before it leaves your device. Redaction that has not been verified is not redaction.
Step by step
- Use a redaction tool, not a drawing tool
Highlighter, pen and shape tools only paint on top. Look for a function actually named redact. - Apply the redaction
Many tools mark first and apply as a separate confirming step. Unapplied marks are just shapes. - Search the document for a word you removed
If it returns no result, the text is genuinely gone. This takes one second and is the only proof. - Check the metadata too
Author name, original filename and revision history live outside the visible page.
Our iOS app for exactly this. Runs on your device — no account, no tracking.