I would say your DNA results are your source documentation, Daiyu.
You should then explain the discrepancy between your birth certificate and your DNA results in your biography or in Research Notes.
As for building your paternal line, you are free to attach either father to your profile; you would select the appropriate relationship, depending on which father you choose. However, for your DNA to propagate properly, you should attach your biological father.
You can create a profile for your other father and connect him in your biography.