How to use pypdf2 to check if a pdf password is correct

I am doing a challenge problem from Automate the Boring Stuff with Python. The task is to write a program that will “brute force” a pdf password using a provided dictionary.txt file.

Using a file I encrypted and know the password to, and a dictionary file that contains that password, I cannot get my code to “figure out” that it is the password. Instead it runs until the end of the dictionary file, then stops.

I thought I might be misunderstanding how pdfObject.decrypt() would work in an “if” statement, so I made a little test program to play with the syntax, but it works in that program using the same syntax as my “main” program. In the “test” program I provide the password from input() instead of argv and a list, but I can’t see if/how that’s affecting it.

#My Program (that blitzes right past the correct password):

#/usr/bin/python

# bruteForce.py - Uses a dictionary attack to crack the password of an
# encrypted pdf

from sys import argv
import PyPDF2

# Take the argument for the file you want to attack and open it
if len(argv) > 1:
    pdfFilename = argv[1]
else:
    print('User must specify a file.')
    exit()

# Open the pdf as an object
pdfFile = open(pdfFilename, 'rb')
pdfObject = PyPDF2.PdfFileReader(pdfFile)

# Add the contents of the dictionary file to a data structure
dictionaryList = []
dictionaryFile = open('dictionary.txt')
for word in dictionaryFile.readlines():
    dictionaryList.append(word)
    wordLower = word.lower()
    dictionaryList.append(wordLower)
dictionaryFile.close()

# Iterate over the data structure, trying each password as lowercase
print('Trying passwords...')
for word in dictionaryList:
    password = str(word)
    print('Trying ' + password)
    if pdfObject.decrypt(password) == 1:
        print('Password is ' + word)
        exit()
    else:
        continue

print('Password not found')

##My Test (that works and returns 'Yup, that's it!'):

#!/usr/bin/python
# Figuring out how to deal with foo.decrypt to get a value of 1 or 0
# This first test returns the correct result with the correct password,
# so presumably bruteForce is not feeding it the right password somehow

import PyPDF2

filename = input('What file?')
password = input('What password?')

pdfFile = open(filename, 'rb')
pdfObject = PyPDF2.PdfFileReader(pdfFile)

if pdfObject.decrypt(password) == 1:
    print('Yup, that's it!')
else:
    print('Nope!')



I expect the program to arrive at the correct word in the dictionary, try it, and stop. Instead, it runs to the end of the list and says "Password not found."