My daughter's biological father is not on the birth certificate, nor has he ever even seen her or cared for her. I am engaged to a wonderful man who considers her his daughter, and we want to make it official once we are married. Could I just add him to the birth certificate as her father? How should I go about doing this? Thanks!

... Could I just add him to the birth certificate as her father? How should I go about doing this? Thanks!

Not a good idea and I'm not sure you could do that anyway. How old is your daughter?

See an attorney about a step-parent adoption. In some states you would have to have been married a year, minimum, but that would be the way to go.

So your question is, can you commit fraud and lie on a legal government form.

No you can not do this. The proper and legal way is to have him adopt the child.
Even if not on the birth certifictate, he has rights he can claim