Titus Vollbracht

A specially crafted PDF document can utilize JavaScript to modify annotation content and then remove the file’s modification status through JavaScript interfaces. This bypasses digital signature verification by concealing document changes, potentially misleading users about the document’s integrity and compromising the trust associated with signed PDFs.

The software allows for signature spoofing through the use of Optional Content Groups (OCG). When OCGs are supported, the state property of an OCG is runtime-only and is not included in the digital signature computation. An attacker can use JavaScript or PDF triggers to change the visibility of OCG content after signing, modifying the visual content of a signed PDF without invalidating the signature. This can lead to a discrepancy between the signed content and what is displayed to the signer or verifier, potentially compromising the trustworthiness of the digital signature.