PD is monitor photo diode. It's usually present with CW laser diodes. From the (scarce) information you gave, I would expect, that the laser diode uses the case as a fourth terminal. If the laser diode anode would be in common with photo diode, it should be clearly said in a datasheet.
Generally you have to assure, that your driver can safely drive the diode. I would expect, that a pulsed diode could be operated without feedback through a monitor diode, but I can't know for sure. You have to check from the driver and diode specification. In any case, the laser diode allowed operation conditions have to be written in the datasheet.