Simplify PDF password unlock with python + bat

environment

Windows 10 (I'm not familiar with Mac / Linux, so I can't support it) python 3.7

table of contents

--Motivation and overview --Directory structure and file contents --Dependent packages --Commentary --Actual usage - Tips

• Notes --Summary --References

Motivation and overview

Due to the influence of the coronavirus, I think that many online classes are being held at universities. I think that most of the lesson materials for that purpose are distributed using the services on campus, but there are teachers who can sometimes put a password on them. It's not good to redistribute it, and you probably want to reject browsing by non-students, but for this, it's quite annoying to enter the password every time you open ***. *** *** Therefore, let's create a PDF with the password unlocked. If you search for "PDF password unlock" etc., you will find various things, but this time, you can unlock the PDF just by dragging and dropping ***. That's why we go through a two-step process.

--Link bat file and python file --Unlock the PDF password (if known)

It can be realized with python alone, but I think that bat is necessary to unlock the password just by dragging and dropping. So let's use python to unlock the PDF password.

Directory structure and file contents

First, the directory structure and the implemented file contents are shown. Interpret the class folder as the folder where the lesson materials are placed.

root/ 　├ main.py 　└ decoder.bat

class/ 　├ password.txt 　└ target.pdf

• Or class/ 　├ password.txt 　└ 0605/ 　　　└ target.pdf It's okay if it looks like this.

main.py

import sys, pathlib

from pikepdf import Pdf


def get_password(folder):
    passfile = None

    found : bool = False
    #First search in the same folder
    for f in folder.glob("*"):
        if "password" == f.stem:
            passfile = f
            found = True

    #If they are not on the same level, search for another level above
    if not found:
        folder = folder.parent
        for f in folder.glob("*"):
            if "password" == f.stem:
                passfile = f

    #If there is no password file in the next higher hierarchy
    if not found:
        return None
    
    #Extract password from file
    with open(passfile, mode="r", encoding="utf-8") as f:
        password = f.read()

    return password

def main():
    #When starting from bat
    try:
        path = sys.argv[1]
    #When running a py file alone
    except:
        print("input target path")
        path = input()

    path = pathlib.Path(path)
    #Reject other than PDF files
    if path.suffix != ".pdf":
        print("Only PDF file accept.")
        sys.exit()
    
    password = get_password(folder=path.parent)
    #If the password file does not exist
    if password == None:
        print("No password file. input password = ", end="")
        password = input()
    try:
        pdf = Pdf.open(path, password=password)
    except:     #If the password is incorrect
        print("failed to open PDF. check password.")
        sys.exit()

    pdf_unlock = Pdf.new()
    pdf_unlock.pages.extend(pdf.pages)
    #Save at the same level as the original PDF
    newname = f"{path.parent / path.stem}-unlocked.pdf"
    pdf_unlock.save(newname)


if __name__ == '__main__':
    main()

decoder.bat

@echo off
Rewrite the rem class part with the full path of the class folder
cd "class"
"main.py" %*

Dependent packages

You can pip. Easy.

pip install pikepdf

Use the library pikepdf to unlock the PDF password. Existed by reference [1]. A sample program is also available here, so please refer to it.

Commentary

About cooperation between bat file and python

If you drag and drop a file such as an image file to the bat file to open it, at the command prompt

C:\Users\user> decoder.bat (Full path of the file)

It looks like. This argument can be received as% * in the bat file. (Actually,% 0 is better ...) (Refer to reference [2] for details)

Pass this argument as is to python. In python you can accept command line arguments as sys. Reference [3] describes the minimum. So, sys.argv [1] contains the argument (file path) passed from the bat file this time.

Remove PDF password

The basic steps are as follows. All variable names are the same as main.py

Open PDF file with password

pdf = Pdf.open(path, password=password)

Prepare a new PDF file

pdf_unlock = Pdf.new()

Copy the pre-opened PDF to a new PDF

pdf_unlock.pages.extend(pdf.pages)

Save new PDF

pdf_unlock.save(newname)

Actually use

1. Prepare the password.

Write the password of target.pdf in password.txt in the directory structure diagram. At this time, as a caveat, do not start a new line. Since the passwords given by most teachers are the same every time, we adopted a mechanism to prepare a password file.
You can type in the command prompt without preparing it, so if the password is different each time, type it at runtime without creating password.txt.

2. Create shortcut

It's a good idea to put a shortcut for decoder.bat on your desktop. It seems more convenient to be able to execute it from the desktop. It is not required separately.

3. Execute

Drag and drop the PDF file onto the shortcut created in step 2. Then the command prompt will be launched (for a moment) and the password-unlocked PDF file will be saved in the same location as the original file.
If you have not created a password file, you will be prompted for it at the command prompt. Please enter.