Function validateVersionRevision

src/security/encryption-dict.ts:381–401

* Validate that V and R values are compatible.

(version: EncryptionVersion, revision: EncryptionRevision)

 * Validate that V and R values are compatible.
 */
function validateVersionRevision(version: EncryptionVersion, revision: EncryptionRevision): void {
  // Valid combinations per PDF spec:
  // V=1 → R=2
  // V=2 → R=3
  // V=3 → R=3 (unpublished, rare)
  // V=4 → R=4
  // V=5 → R=5 or R=6

  const valid =
    (version === 1 && revision === 2) ||
    (version === 2 && revision === 3) ||
    (version === 3 && revision === 3) ||
    (version === 4 && revision === 4) ||
    (version === 5 && (revision === 5 || revision === 6));

  if (!valid) {
    // Be lenient - warn but allow (some PDFs have weird combinations)
    // In strict mode, we'd throw here
    console.warn(`Unusual V/R combination: V=${version}, R=${revision}`);
  }
}

/**
 * Check if a dictionary represents an encrypted document.