Function compute_encryption_key 

pub fn compute_encryption_key(
    password: &[u8],
    owner_key: &[u8],
    permissions: i32,
    file_id: &[u8],
    revision: u32,
    key_length: usize,
    encrypt_metadata: bool,
) -> Vec<u8> 

Compute the encryption key from a password (Algorithm 2).

PDF Spec: Section 7.6.3.3 - Algorithm 2: Computing an encryption key

Arguments

• password - User or owner password (up to 32 bytes)
• owner_key - 32-byte owner password hash from encryption dictionary
• permissions - User access permissions (P field)
• file_id - First element of file identifier array
• revision - Encryption revision number (R field)
• key_length - Key length in bytes
• encrypt_metadata - Whether to encrypt metadata

Returns

The derived encryption key