I wanted to no how do I go about getting my son father name on the birth certificate. He was away in japan when I had our son and I didn't want him to miss the opportunity to sign.our first born certificate so I left it blank for this day that he is home. Please help. How do I go about it in Philadelphia, PA?

http://fjd.phila.gov/pdf/brochures/dr/Paternity-Brochure.pdf
After leaving the hospital, if both parties wish to
File a voluntary Acknowledgment of Paternity as
To the identity of the father, it will be necessary
To contact the Department of Public Welfare,
Bureau of Child Support Enforcement at 800-
932-0211, for forms and instructions. The
Department of Public Welfare will notify Vital
Records that an Acknowledgment of Paternity
Has been filed. The Division of Vital Records
Will then add the father’s name to the child’s
Birth record. At that time, the Division of Vital
Records will issue a certified copy listing both
Parents’ names at no charge.