Your PDF says AES-256. The key had 9 bits of entropy.
MuPDF called it AES-256. The key came from a timestamp-seeded LCG with 9 bits of entropy: 512 candidate keys, 7 ms to generate them all, and I decrypted my own password-protected PDF in 0.63 s without the password. Foxit's version hashes the literal string "there". The full lab, reproducible.
🎯 Vulnerability: Web Security Vulnerability
💡 Defense Fix: Implement strict input validation, contextual output encoding, and enforce least-privilege authorization controls.