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I am an recent graduate in pure mathematics who only has taken few basic programming courses. I am doing an internship and I have an internal data analysis project. I have to analyze the internal PDFs of the last years. The PDFs are "secured." In other words, they are encrypted. We do not have PDF passwords, even more, we are not sure if passwords exist. But, we have all these documents and we can read them manually. We can print them as well. The goal is to read them with Python because is the language that we have some idea.

First, I tried to read the PDFs with some Python libraries. However, the Python libraries that I found do not read encrypted PDFs. At that time, I could not export the information using Adobe Reader either.

Second, I decided to decrypt the PDFs. I was successful using the Python library pykepdf. Pykepdf works very well! However, the decrypted PDFs cannot be read as well with the Python libraries of the previous point (PyPDF2 and Tabula). At this time, we have made some improvement because using Adobe Reader I can export the information from the decrypted PDFs, but the goal is to do everything with Python.

The code that I am showing works perfectly with unencrypted PDFs, but not with encrypted PDFs. It is not working with the decrypted PDFs that were gotten with pykepdf as well.

I did not write the code. I found it in the documentation of the Python libraries Pykepdf and Tabula. The PyPDF2 solution was written by Al Sweigart in his book, "Automate the Boring Stuff with Python," that I highly recommend. I also checked that the code is working fine, with the limitations that I explained before.

First question, why I cannot read the decrypted files, if the programs work with files that never have been encrypted?

Second question, Can we read with Python the decrypted files somehow? Which library can do it or is impossible? Are all decrypted PDFs extractable?

Thank you for your time and help!!!

I found these results using Python 3.7, Windows 10, Jupiter Notebooks, and Anaconda 2019.07.

I was using the following code mainly taken from DuckPuncher's answer to this post Extracting text from a PDF file using PDFMiner in python? to convert pdfs to text files: