前女友发来加密的"520快乐.pdf",我用python破解开之后,却发现

PS D:\> pip install PyPDF2
Looking in indexes: http://mirrors.aliyun.com/pypi/simple
Collecting PyPDF2
  Downloading http://mirrors.aliyun.com/pypi/packages/b4/01/68fcc0d43daf4c6bdbc6b33cc3f77bda531c86b174cac56ef0ffdb96faab/PyPDF2-1.26.0.tar.gz (77 kB)
     |████████████████████████████████| 77 kB 919 kB/s
Using legacy 'setup.py install' for PyPDF2, since package 'wheel' is not installed.
Installing collected packages: PyPDF2
    Running setup.py install for PyPDF2 ... done
Successfully installed PyPDF2-1.26.0
PS D:\>

import PyPDF2
#加密PDF
def encrypt(old_Path, new_Path):
    """
    :param old_Path: 待加密文件的路径名
    :param new_Path: 加密之后的文件路径名
    """
    with open(old_Path, 'rb') as pdfFile: 
        pdfReader = PyPDF2.PdfFileReader(pdfFile)
        # 创建pdfWriter对象用于写出PDF文件
        pdfWriter = PyPDF2.PdfFileWriter()
        # pdf对象加入到pdfWriter对象中
        for pageNum in range(pdfReader.numPages):
            pdfWriter.addPage(pdfReader.getPage(pageNum))
        # 密码设置为8888
        pdfWriter.encrypt('8888')
        with open(new_Path, 'wb') as resultPDF:
            pdfWriter.write(resultPDF)
            print('加密成功!')

#你可以根据需求，自己定义密码的位数，这里只定义4位纯数字密码
for i in range(10000):
	#生成四位数密码
	pwd=str(i).zfill(4)
	print(pwd)

def decrypt(old_Path, new_Path):
    """
    :param old_Path: 待加密文件的路径名
    :param new_Path: 加密之后的文件路径名
    """
    with open(old_Path, 'rb') as pdfFile:
        pdfReader = PyPDF2.PdfFileReader(pdfFile)
        pdfWriter = PyPDF2.PdfFileWriter()
        # 判断文件是否加密
        if pdfReader.isEncrypted:
            # 判断密码是否正确
            for i in range(10000):
                #生成四位数密码
                pwd=str(i).zfill(4)
                if pdfReader.decrypt(pwd):
                    for pageNum in range(pdfReader.numPages):
                        pdfWriter.addPage(pdfReader.getPage(pageNum))
                    with open(new_Path, 'wb') as resultFile:
                        pdfWriter.write(resultFile)
                        print('成功了!密码是：'+pwd)
            else:
                print('密码错了!哼~~~')
        else:
            print('没有加密呀~~~')