Function getFileKey

getFileKey(
    userPassword: ByteArray,
    ownerPassword: ByteArray,
    u: ByteArray,
    ue: ByteArray,
    o: ByteArray,
    oe: ByteArray,
): Promise<ByteArray>
Retrieves the file encryption key using user or owner password. Tries owner password first, then falls back to user password.
Parameters
- userPassword: ByteArray
  The user password to try.
- ownerPassword: ByteArray
  The owner password to try.
- u: ByteArray
  The 48-byte /U value from the encryption dictionary.
- ue: ByteArray
  The 32-byte /UE value (encrypted user key).
- o: ByteArray
  The 48-byte /O value from the encryption dictionary.
- oe: ByteArray
  The 32-byte /OE value (encrypted owner key).
Returns Promise<ByteArray>
A promise that resolves to the 32-byte file encryption key.
Throws
Error if both passwords are invalid.
Example
```
const fileKey = await getFileKey(userPw, ownerPw, U, UE, O, OE)
```
- Defined in packages/pdf-lite/src/crypto/key-derivation/key-derivation-aes256.ts:154