What is your PDF
hiding from you?
AI tools can read text that is completely invisible to the human eye — including secret instructions embedded by bad actors to manipulate how the AI analyzes your documents. This tool shows you everything. Learn how it works ↓
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How it works
PDF X-Ray uses PDF.js to read the raw text layer of your document — the same data that AI assistants process when you share a PDF. It checks every text item against four known techniques used to hide content from human readers while keeping it fully machine-readable.
Tiny font size
Text rendered at font sizes below 3pt is effectively invisible to the naked eye but fully readable by AI. A document can embed entire paragraphs of hidden instructions at 0.1pt — too small to see, but present in the text stream.
Off-page positioning
Text placed at coordinates outside the visible page boundaries never appears on screen or in print, but stays in the document's content stream. AI assistants process it alongside the visible content.
White text
Text colored to match the page background is invisible unless selected with a cursor — a classic trick that fools human readers but not AI models, which read color-blind from the raw text layer.
Invisible rendering mode
The PDF specification includes a text rendering mode that hides text from being drawn on screen while keeping it in the content stream. The text is completely invisible in any viewer but still present for AI to read.