This question is most relevant for when you run into conflicts between Python 3.X and 2.7. There are several ways in which you can ensure that you are using the right version of python:

1. You can rename the versions of python to something other than python in their respective installations.
2. You can create a virtual environment using venv for Python 3 or virtualenv for Python 2 and select your your required version.
3. You can use pyenv to set a local Python version, this should allow you to test without getting the different versions mixed up.
4. If you would like, you can create your own Wrapper for PDFTron SDK using your preferred version of Python.