Currently documents can be sent to be signed with strong authentication in Finland, Sweden, Norway and Denmark. In order to sign a document with strong authentication, the recipient must have one of the following:

• Finnish personal identity code and Finnish bank IDs or mobile ID

• Swedish personal ID and BankID 

• Danish personal ID and NemID 

• Norwegian BankID

If the signer owns none of the above, you can ask her/him to sign it without strong authentication.