Walther manufactured the PP series until the end of WWII. Post war production was carried out by Manurhin in France, under license of Walther. Eventually, Walther began manufacturing the guns in Germany again. German made Walthers are the most desirable.
Just to add some detail to what Lew said.
The PP was released in 1929 and the PPK in 1931.
The PP and PPK were produced before and during WW II by Walther in Germany. I understand that in the later stages of the war, quality declined. I have no confirmation of this. Whether this adversely affects the value of those later pistols I don’t know.
After the war Germans were not allowed to manufacture arms. Walther therefore licensed the French company Manufacture de Machines du Haut-Rhin, shortened to Manurhin, to produce PP and PPK pistols. These were produced in the factory at Mulhouse-Bourtzwiller, France not very far from the Walther factory in Ulm, Germany. These guns were clearly identified as being made in France under licence. They did not show the Walther banner.
Later, German companies were allowed to re-commence production of arms. For some time after this Walther made the forgings which were sent to Manurhin for machining. The soft or unhardened slides were then returned to the Walther factory at Ulm where they were roll marked and hardened. They then completed the final assembly, testing and proofing. Under German law, because the final work was completed in W Germany, they were entitled to mark the guns as having been made by Walther in Germany.
Possibly at the same time, Manurhin continued making pistols entirely in France, and these were tested and proofed in France. They will have the St Etienne proof mark. French made guns were not entitled to show the Walther banner.
Later on, in the late '80s, Walther began making them from scratch. It is felt by some that they were not as good as the earlier jointly produced pistols.
I cannot fault my Manurhin PP, but I am no expert. Markings in the box suggest it was made in 1973. It is totally French, unlike me.
I cannot claim credit for compiling this information. I got most of the info from the Walther forum
The 'Manurhin myth' explained - WaltherForums and hope that MGMike and Searcher451 do not mind me condensing the Sticky posted there. I apologise to them and to readers if I got anything wrong.