You must always carry a valid passport when entering and leaving Denmark, and it must remain valid for the duration of your stay. This also applies to trips to Greece. Therefore, it is a good idea to check your passport’s validity well in advance of your departure.
If you reside in Greece and plan a vacation in Denmark, it may be wise to renew your passport while you are there. All Danish citizens can generally apply for a new passport at any Citizen Service Center in Denmark – it is cheaper, and the processing time is shorter than at the Danish Embassy in Athens.
Read more about the rules for issuing and renewing passports in Denmark here.
Read more about the rules for issuing and renewing passports at the Danish Embassy in Athens here.