What hidden information is in your PDF — and how to remove it

When you send a PDF, you send more than the pages. Most PDF files carry a small block of document information — and some carry content that is hidden but still present. Usually it is harmless. Occasionally it reveals a client's name from the template you reused, or the text you thought you had blacked out.

What a PDF can contain besides the pages

• Title, author, subject and keywords — often filled in automatically from your account name or an old template.
• Creator and producer — the software and version used to make the file.
• Creation and modification dates.
• Form fields whose values can still be changed.
• Text hidden under boxes or images, which can be selected and copied.

How to check

Open the PDF in your reader and look at File → Properties (or Document Properties). Then press Ctrl+A (Cmd+A on a Mac) and copy everything into a text editor: if text appears that you can't see on the page, it is hidden, not removed.

A safe cleaning routine

1. Remove pages you don't intend to share with Remove Pages.
2. If you covered text in an editor, run Flatten PDF in lock mode so the page becomes an image and the covered text is genuinely gone.
3. Run Clean PDF to erase title, author, subject, keywords, creator and producer fields.
4. Re-open the result and repeat the properties and select-all checks.

Drawing a black rectangle over text is not redaction. Unless the page is flattened to an image, the original text usually remains underneath and can be copied.

When it matters most

Legal filings, job applications sent from a work computer, documents published on a website and anything derived from another client's template are the usual risks. The checks above take a few minutes and run entirely in your browser with PDFQuick, so the sensitive file isn't uploaded in the process of cleaning it.