DopplerPSK is an experimental program for transmitting Doppler-corrected PSK31 on satellite uplinks. It uses an orbital propagator to estimate the Doppler shift for your location so that it presents a constant frequency from the point of view of the satellite's transponder. It is primarily designed is for satellites that have a SSB uplink receiver and an FM downlink (which is free of Doppler shift at the baseband receiver due to the FM subcarrier).
DopplerPSK does not provide any PSK31 demodulation; you should use a separate program for that purpose. DopplerPSK does not provide any compensation for downlink Doppler (which you would need for fully linear transponders).