Both .pz2 and .pz3 are files come from Poser 3D computer graphics software and if any kind of pz2 to pz3 conversion is even possible, it would be used with this software.
We have not found any relevant information about this conversion beyond the fact from where these files come from. If you need help with something specific or face particular issue, it might be best to reach out to Bondware support.
Updated: October 27, 2023