Austria. But I think its also true for germany. There is a legal difference between biological, social and legal father.
Just beeing the biological father grants no nothing at all its just important to know who has to pay the upkeep.
Friends of mine had to do this. Did not marry and he had to adopt their daughter right after birth. Thats a reason why a lot of couples marry here before the child is born. Too much paperwork if you do not.