can you please meassure the length without fuze adapter?
It is Czech Vz.08 projectile used by Kingdom of Yugoslavia Army prior to WWII, but I am not sure whether it was used by Wehrmacht. Shell Vz.25 7,65mm designated as 8cm Sprgr. M25 (j) by Germans definitely is.
The case was marked Dusseldorf in 1917 and above 38. It is certain, a German shell originally.