Hi Yannis
PDEP are the latin initials for Pro Deo et Patria = For God and Fatherland, a motto much used by Orders and other forces.
In this link you will find all the various marking combinations, both maker's and blade inspector's, through all Klingenthal existance. With a bit of patience, you may be able to precise the date of your sword.
http://www.chez.com/klingenthal/
Kind regards