The baby is several months old when my character makes his mind up what to do about it. Once he has acknowledged paternity, can his name be retroactively entered on the birth certificate as the father, and could the boy be given his surname? What documentation will he need to enter into with the baby's mother? He wants to keep it all as informal as possible, and as he has a good income he is quite prepared to be generous - within limits. He is happy to support the child, and willing to have contact with him as the boy grows older, but wants to keep contact with the mother minimal and at arms' length as much as possible.
Is this scenario generally feasible, and what would be the absolute minimum legal requirement for my character to accept paternity and take financial responsibility for the child?