Form for Ordinary Certificate of Acknowledgment. (Personalized Seal).An Acknowledgment of Paternity (AOP) is a legal document that allows parents who aren't married to establish legal paternity. An acknowledgment is one of the most common types of notarial acts, but it often confuses Notaries. Here are 5 steps to performing an acknowledgment. Check out our letter of acknowledgement template selection for the very best in unique or custom, handmade pieces from our templates shops.