The scenario describes a cryptographic attack where the attacker (in this case, the student) uses a predefined list of commonly used passwords to try and unlock a secured PDF document. This technique is known as a Dictionary Attack.

According to the CEH v13 Official Courseware:

A Dictionary Attack is defined as “a method of breaking passwords by trying out a predefined list of words (dictionary) commonly used as passwords.”

Unlike a brute-force attack, which tries every possible character combination, a dictionary attack relies on known or likely password choices, which makes it faster but less exhaustive.

Dictionary attacks are commonly used against encrypted or password-protected files, login forms, and even hashes.

Relevant distinctions from other options:

A. Man-in-the-middle attack involves intercepting communication between two parties and is unrelated to offline password cracking.

B. Brute-force attack tries all possible character combinations, not just a list of known or common passwords.

D. Session hijacking involves taking over a user session and is unrelated to document password cracking.

Reference – CEH v13 Official Study Materials:

Module 20: Cryptography

Section: "Cryptanalysis Techniques"

Subsection: "Dictionary Attack vs. Brute-force Attack"

CEH v13 eBook or Study Guide — look for Table: “Types of Password Attacks” under “Cryptography Attack Vectors”

This exact technique is illustrated in CEH v13 labs involving John the Ripper, Hydra, and password recovery tools.