I just installed this (see below) and it works fine. Are you sure that your Python paths are set correctly in your environment? You could try to run 'pip uninstall pdf2docx' and then re-install it.
Another way to test this would be to use a Python 'virtual' environment as described at venv — Creation of virtual environments — Python 3.9.9 documentation
]. That is what I just did and had it set up and tested in a couple of minutes.