Can I Let My Fiance Sign My Daughter's Birth Certificate?

Most importantly, do you live in New Jersey? At the end of your question, you reference a request for child support from the biological father - which says that you already opened a child support case in the court system and have a state agency/probation seeking to recoup monies from him for your child. If you have already filed a complaint with the court system for child support or if you are receiving governmental assistance for your child and identified the biological father as the responsible party for payment purposes, simply adding your fiance to the birth certificate does not / will not resolve all of the issues. If anything, it can cause you more issues if you are receiving government benefits and previously identified the other guy for payment purposes. The simplest solution is to have the biological father sign a written certification stating that he agrees to relinquish his custodial rights to the child and effective with the entry of an order permitting your fiance to adopt the child,  he will be relieved of any legal obligation. You can also include in that certification that he agrees to cooperate with the adoption process and to sign any and all papers required of him. I have no idea why your fiance has an issue with child protective services but if he is going to be around your son on a daily basis and is a good father to him, I dont think that you should be afraid to permit a home visit as part of that adoption process.