There is no reason for you to sign such a document. Since you and the mother were never married, she has custody pursuant to statute. Although she has custody, you should still have some input on major decisions regarding your child. What you do need is a Court determination that you are the father so that if something should happen to the child's mother (if she died or became incapacitated) you would be able to step in rather than having to wait until it could be determined that you are the father. If there has been an action to set child support, part of that order would have been a finding of fact and conclusion of law that you are the child's father. If your name is on the birth certificate, that would also indicate that you are the father.
As to "sole custody" or "joint custody", that is always before the Court and you could seek to have the custody characterized as "joint", but in practice that really means very little since the mother would have the final say. And, "sole custody" or "joint custody", you should be consulted on MAJOR issues: surgery, quitting school, etc.
Legal disclaimer: Janne Berry Osborne is an attorney duly licensed to practice law in the State and Federal Courts of South Carolina, including the Bankruptcy Court. This answer is offered for general educational and informational purposes only. It is not offered as, and does not constitute, legal advice nor does it constitute or create an attorney-client relationship between Janne Berry Osborne and any other person. You should schedule a consultation with an attorney to discuss your specific legal issues.
I agree with Ms. Osborne's response - this document does not change what already exists if the child is living with her. If he is she already has custody. Perhaps she believes if you sign it she does not have to consult you about raising your son. For that reason alone - that she may believe she could cut you out of his life - you should not sign it.
If you are not on the birth certificate or paying child support (paternirty may have been established in the support order) will she deny you are the father? If she does you may have to establish paternity in a later court action but once that is done you can always seek joint custody. Depending on the order of the judge that may not give you any greater rights or privileges in being in your son's life but it would set out exactly how you two would proceed to raise your son.
I hope that is not necessary and you two can work through all the issues that arise in raising a child. if you can not court is always an option.
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