pip install pypdf2

from PyPDF2 import PdfFileReader

filename = "test.pdf"
reader = PdfFileReader(filename)

# 不解密可能会报错：PyPDF2.utils.PdfReadError: File has not been decrypted
if reader.isEncrypted:
    reader.decrypt('')

page = reader.getNumPages()
print(page)

"""
如果加密是高版本的（3, 4），可能会报错
NotImplementedError: only algorithm code 1 and 2 are supported

原因是：
代码中有版本判断
if not (encrypt['/V'] in (1, 2)):
    raise NotImplementedError("only algorithm code 1 and 2 are supported")
"""

pip install pdfplumber

import pdfplumber

filename = "test.pdf"
f = pdfplumber.open(filename)
print(len(f.pages))