can the bio father stop a stepparent adoption after its finalized?

What is the name of your state?
wisconsin
the bio father voluntarily gave up his parental rights and the adoption and termination of his rights were done on feb 25, 2004 and now he is saying he is going to stop the adoption. Is there anything he really can do or not? i dont want to sit here and worry about it forever now. he has a very bad criminal past and i am afraid that he can do something to ruin the adoption by my husband.

There is a period of time that you get to change your mind about the adoption and can have it stopped or changed or whatever. That time period varies from state to state. Also, whether or not he can get it stopped will depend on other things.

If you had an attorney handle this, the best thing to do is to call him or her back and ask or research your state's laws regarding adoption and relinquishment of parental rights.

I agree with Grace and would point you to http://www.wisbar.org/res/sup/2001/00-1739.htm for further understanding of the complexity of this question.