In Patula v. People (685 Phil. 376), the Supreme Court explained the nature of a self-authenticating document:
The nature of documents as either public or private determines how the documents may be presented as evidence in court. A public document, by virtue of its official or sovereign character, or because it has been acknowledged before a notary public (except a notarial will) or a competent public official with the formalities required by law, or because it is a public record of a private writing authorized by law, is self authenticating and requires no further authentication in order to be presented as evidence in court. In contrast, a private document is any other writing, deed, or instrument executed by a private person without the intervention of a notary or other person legally authorized by which some disposition or agreement is proved or set forth. Lacking the official or sovereign character of a public document, or the solemnities prescribed by law, a private document requires authentication in the manner allowed by law or the Rules of Court before its acceptance as evidence in court. The requirement of authentication of a private document is excused only in four instances, specifically: (a) when the document is an ancient one within the context of Section 21, Rule 132 of the Rules of Court; (b) when the genuineness and authenticity of an actionable document have not been specifically denied under oath by the adverse party; (c) when the genuineness and authenticity of the document have been admitted; or (d) when the document is not being offered as genuine.
