When you see "UPD" attached to software keys online, it usually means "updated." Website owners use this term to lure people looking for working serial numbers, cracks, or key generators (keygen).
To understand why the Pro version is highly sought after, it helps to compare what you get in the free version versus the premium upgrade. Free Version Features Basic pen and highlighter tools. Core color palette (limited selection). Eraser tool. Screenshot crop tool. Touchscreen and pressure-sensitivity support. Pro Version Features Epic Pen Pro Activation Key UPD
Change colors and brush sizes on the fly. When you see "UPD" attached to software keys