The Walther PP series has been around for a long time. Introduced during the 1930's, saw considerable military use during WW2, manufactured in France (Manhurin) after WW2 before the Walther works came back into operation. PP= Pistole Poleizi (Police Pistol), PPK= Pistole Poleizi Kurtz (Police Pistol, Short), and PPK/S = the PPK upper mounted on the PP lower to comply with US import restrictions during the 1970's, various calibers including 9X17 (.380ACP), 7.65mm (.32ACP), and .22LR. At one time a target version was marketed in .22LR with extended barrel and adjustable sights. German Walthers and the French Manhurin pistols were shipped with the factory test targets, at least some indication of each pistol's potential performance.
Generally considered to be an excellent design, known for reliability and good accuracy, fairly simple to operate and maintain. Moderately heavy when compared to alloy and polymer framed guns so common these days, but not overly so. These pistols operate on the blowback principle (recoil operated, fixed barrel) so recoil can be quite sharp, especially in .380, which some find surprising at the first experience. Double action trigger pulls are typically rather heavy, but usually smooth and controllable with a bit of experience. Single action pulls are usually fairly crisp, but with a fair amount of take-up and overtravel. In short, there is a learning curve that requires training and practice.
I've owned several over the years. One thing sticks out in my mind; as a 1911 shooter I am accustomed to taking a high grip on the pistol. With the PP-series pistols this can result in the slide cutting the flesh of the hand as it cycles. I recall having to consciously overcome my tendency to grip the pistol as I would a 1911, Browning Hi Power, etc.