Briefly
The earliest VAG TDI engines, TDI 90 and TDI 110, are non-PD. They use a conventional diesel distributor pump system driven off the toothed cambelt. Injection quantity and timing are set at the pump and each injector has a separate feed line from the pump.
The more recent VAG TDIs, including 100, 105, 115, 130, 150 and 160 BHP engines, are PD (Pumpe Duese, best translated as Pump Injector). Fuel is distributed by a low-pressure pump and common fuel rail to individual injector assemblies attached to each cylinder head. Injection quantity and timing is set at the injector. Stripped of all their complex engineering detail, the injectors are just like a stirrup pump or a syringe squirting fuel through a spray head into the cylinder. Of course, the complex engineering detail is what makes it work reliably for hundreds of thousands of miles
The injectors are driven by extra lobes on the single camshaft. These lobes are very high-lift, and even though the cam followers have rollers, they are very highly stressed and require special high-grade oil to avoid premature wear.
There was a PD TDI 90 but apparantly it was only fitted to VW Sharans.
All of these engines have their injection timing and quantity parameters finely tuned by electronic actuators that modify the basic mechanical delivery.
The best way to tell whether your engine is PD or not is by engine code, but I haven't found a list yet which distinguishes between PD and non-PD TDI engines. I might put one together - but not today, the boss might notice