A PDF prompt injection hides instructions inside a document — usually as invisible, white, or tiny text — so a human reader never sees them, but AI that reads the PDF's text (a resume screener, summarizer, or other AI tool that reads documents) picks them up and may follow them. PDFBook's Detect Hidden Text tool surfaces this hidden text so you can see what an AI would actually read.

Open PDFBook's Detect Hidden Text tool, drop in your PDF, and click Process. It scans every page for invisible, transparent, white, near-zero-size, and off-page text, then downloads a report listing each finding with the page number, why it was hidden, and the hidden text itself. It runs entirely in your browser, so even sensitive PDFs stay private.

Many modern systems can, and PDFBook makes it easy to check yours. White-on-white or tiny keyword stuffing is a long-standing resume trick that increasingly backfires. Run your resume through the Detect Hidden Text tool to see exactly what hidden text it contains before a recruiter or ATS flags it.

Yes. PDFBook processes the file entirely in your browser and never uploads it. The tool only reads and extracts text — it does not run anything inside the PDF — so it is a safe way to inspect a suspicious or untrusted document.