If you can have the biological father voluntarily sign a consent to the adoption and termination of his rights, this is helpful. Otherwise, you would need to file a petition with the Orphans Court in your county for an involuntary termination of the biological father's rights based on the PA code (reasons can be no contact, no support, etc.).
Best to consult an attorney for the filing of the paperwork. You and your spouse (step-parent) will be subject to a federal background check.