Which cryptography attack is the student attempting?

A computer science student needs to fill some information into a secured Adobe PDF job
application that was received from a prospective employer. Instead of requesting a new document
that allowed the forms to be completed, the student decides to write a script that pulls passwords
from a list of commonly used passwords to try against the secured PDF until the correct password
is found or the list is exhausted.
Which cryptography attack is the student attempting?

A.
Man-in-the-middle attack

B.
Brute-force attack

C.
Dictionary attack

D.
Session hijacking