The goal of this clinical research is to learn about the safety and tolerability of Keytruda® (pembrolizumab) in combination with paricalcitol, with or without standard chemotherapy in patients who have resectable (can be removed with surgery) pancreatic cancer. In this study, standard chemotherapy is the combination of Gemzar® (gemcitabine) and Abraxane® (nab-paclitaxel).