see - sc.judiciary.gov.ph/jurisprudence/2013/july2013/181163.pdf
"x x x.
"The nature of documents as either public or private determines how the documents may be presented as evidence in court. Public documents, as enumerated under Section 19,33 Rule 132 of the Rules of Court, are self-authenticating and require no further authentication in order to be presented as evidence in court.34
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 authentication35
in the manner prescribed under Section 20, Rule 132 of the Rules:
SEC. 20. Proof of private document. – Before any private document offered as authentic is received in evidence, its due execution
and authenticity must be proved either:
(a) By anyone who saw the document executed or written; or
(b) By evidence of the genuineness of the signature or handwriting of the maker.
Any other private document need only be identified as that which it is claimed to be.
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 21,36 Rule 132 of the Rules; (b) when the genuineness and authenticity of the 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.37
Indubitably, Marine Certificate No. 708-8006717-4 and the Subrogation Receipt are private documents which Philam and the consignee, respectively, issue in the pursuit of their business. Since none of the exceptions to the requirement of authentication of a private document obtains in these cases, said documents may not be admitted in evidence for Philam without being properly authenticated.
x x x."
