Does anyone of you know how and where I can download postal area districts of Germany in shapefiles (download free of charge if possible).
You find a dowload here : http://arnulf.us/PLZ However, the data is from 1999 and I'm not sure if it still is up-to-date.
Arnulf Christl's personal website arnulf.us, which contains the description of his public domain dataset of German postal codes, is unavailable at the moment. You can find an archived version at the Wayback Machine.
A different dataset is a GeoJSON file of postal codes extracted from OpenStreetMap by the German company Folge 3. It's a bit patchy, and not quality controlled (it includes some Spanish postal code areas, for example).
the zip-code from Arnulf 1999 is too old, i was used this file but it was wrong - for 5digits - i check with this svg - map http://www.maps4office.com/interaction-svg-maps/ - and level 8 (zip-code) was right.
my german is not good but i change to DE: http://www.maps4office.de/shop-detail/deutschland-citymarker/citymarker-de-postleitzahlen-fuenfstellig/ and the map is from 2014 ... but it's not free