One PDF, two readers: humans see pages, machines get clean Markdown (sgaud.com)
Adaptive PDFs attach Markdown-formatted replacement text to a PDF's content via marked-content sequences — a feature in the spec since PDF 1.4. Renderers ignore it and show the normal page; extractors like PyMuPDF get clean headings, lists and tables instead, with under ~10% file-size overhead.
One Rust dev flipped it instantly: the same layer that feeds an LLM clean structure can feed it a malicious instruction a human would never see — invisible prompt injection in your electricity-bill PDF.
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