You are a citizen of a Nordic country and are at least 18 years of age.
You have become a citizen of a Nordic country not by application but by some other way.
You have lived in Finland for the past five years.
You have not been sentenced to imprisonment during the past five years.
Valid passport or other official ID
Proof of continuous residence in Finland (typically registered address history from the Finnish Population Information System)
Birth certificate and possibly a certificate proving current citizenship.