What is the difference between a C-visa and a D-visa?
A C-visa is for short-term stays ("short-stay visa"). With a C-visa, the total length of your stay in the Schengen area cannot exceed 90 days during any period of 180 days. The rules for C-visas are the same in all Schengen countries.
A D-visa is a visa for long-term stays ("long-stay visa"). Each Schengen country decides on its own requirements for a D-visa. Norway issues D-visas as entry visas, which most often goes to people who were recently granted a residence permit or who lost their residence card. The type of D-visa Norway issues allows you to travel in transit through other Schengen countries on your way to Norway.