Can you get a legal document on line that can be filled out between an unmarried couple in regards to custody, property etc. ? Can this form be taken

You can get plenty of legal documents on the internet.  Whether they conform to your state and county can not be determined unless you check it against the rules that pertain to your jurisdiction.  Having something notarized does not make it binding before the courts, unless it conforms and is filed with the court.  In order to file such a document with the court, you would first need to initiate some sort of action, be it custody or a civil case.