What your PDF is hiding

Seven places names and numbers hide inside a PDF — how to check yours, and what our Redact tool removes.

The short version

A PDF is more than what you see on the page. Names, numbers and notes can sit in form fields, metadata, bookmarks, links, comments, attachments — and under black boxes that only look like redactions. Before you share a sensitive PDF, know where to look.

7 places a PDF can hide data

  1. Text under a black box. A rectangle drawn on top of text hides it from the eye, not from the file. The words are still there and can be selected, copied or searched. In 2019, a court filing by Paul Manafort's lawyers made the news because the "redacted" passages could simply be copied out.

  2. Hidden text layers. A PDF page isn't a picture — it's a list of drawing instructions: "write this text here", "draw this image there". Some instructions put text on the page that your eyes never see, but search, copy and paste do:

    The OCR layer under a scan. A scan is a photo with no text in it. When a scanner or app runs OCR, it lays invisible text over the photo, word for word, so you can search and copy. On its own, the OCR layer just repeats what you see. The risk starts when someone covers part of the scan: the box hides the photo, but the invisible text underneath is still there — and still found by search.

    White text. Text coloured white on a white page. Often left over from templates — "[Client name]" turned white instead of deleted — and sometimes hidden on purpose.

    Text under an image. Text drawn first, then covered by a stamp, a logo, a white rectangle or a pasted screenshot. You see the picture; the text beneath it is intact.

    Rarer cases: text placed outside the visible page, or set at a tiny size. All of this is part of the page itself — separate from metadata, bookmarks and attachments.

  3. Form fields. What someone typed into a form — name, ID number, address — is stored separately from the page text. Covering it on the page does not delete it.

  4. Metadata. Every PDF has hidden properties: author, title, subject, keywords, the software used, creation and edit dates. A title like "Claim against J. Smith" travels with the file.

  5. Bookmarks. The outline in the sidebar can name people or matters — "Contract with Ivanov", "Patient 0412".

  6. Links and comments. A link can point to mailto:name@company.com; sticky notes and review comments often contain names and opinions nobody meant to send.

  7. Attachments. A PDF can carry whole files inside it — a spreadsheet, an email, an earlier draft.

How to check your own PDF

  • Properties: in Adobe Reader, File → Properties; in Preview on a Mac, Tools → Show Inspector. Look at author, title, subject and keywords.
  • Select all: press Ctrl+A (⌘A on a Mac) and copy into a text editor. Anything that appears there is in the file — including text under boxes or behind images.
  • Sidebar: open the bookmarks, attachments and comments panels in your PDF reader.
  • Search: search the file for a name you blacked out. If it's found, it's still there.

What StayPutPDF Redact removes

In every redacted file

Redact builds a brand-new PDF and copies only the pages into it. Links, comments, form fields and their values, bookmarks, attachments and the original metadata (author, title and the rest) are not carried over. The new file's properties only show the software that made it and the date.

On pages with a black box

The page is re-drawn as an image with the box burned in. The covered text is gone from the file — and so is any hidden text layer on that page. These pages lose selectable text.

Want the strongest result? Tick "Flatten every page" — every page is re-drawn as an image, so no selectable or hidden text is left anywhere in the file.

What it doesn't do — honestly

  • Pages without a box stay as they were, including any hidden text layer on them. If you're not sure what a page contains, use "Flatten every page".
  • Automatic search only finds real text, not words inside scanned images or photos — draw boxes over those by hand.
  • Links and form fields stop working in the redacted file, because they're removed. Keep your original if you still need them.

After redacting, run the checks above on the new file. The final check is yours.

This page is general information about how PDF files work, not legal or compliance advice.

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