Free tool · Document security

Is your PDF hiding instructions for AI?

Hidden text can tell an AI assistant to skip a clause, change its advice or leak data. Drop a PDF and see in seconds what a human reader can't.

  • Free, no sign-up
  • Files never stored
  • Processed in the EU
  • Results in seconds

Drop a PDF here

or click to choose a file · up to 10 MB and 50 pages

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Your file is checked in memory and deleted right away.
What we check

The tricks a human reader never sees

AI assistants read every character of a document, including the ones hidden from you. Attackers use that to slip in instructions. The checker looks for the most common techniques.

  • White or invisible text

    Text in the same colour as the background, or set to be invisible, that only software reads.

  • Tiny or off-page text

    Characters too small to see, or placed outside the visible page.

  • Covered text and hidden layers

    Text hidden under images or shapes, or in layers that are switched off.

  • Metadata and comments

    Instructions tucked into the document properties, annotations or form fields.

  • Invisible Unicode

    Characters that don't print but still carry a message for AI models.

  • Scripts and attachments

    JavaScript, automatic actions and embedded files that can harm your computer.

The checker uses automated analysis and may not catch every technique. A clean result is not a guarantee that a document is safe. Files are processed in memory on servers in the EU and are not stored.