2819. To be authentic, a notarial act shall be signed by all the parties; it then makes proof against all persons of the juridical act which it sets forth and of those declarations of the parties which directly relate to the act.
Where the parties are unable to sign, their declaration or consent shall be given before a witness who signs. Minors, persons of full age who are unable to give consent and persons who have an interest in the act may not be witnesses.