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