Presumption of documentary truth shifts the evidential burden and permits admission of otherwise admissible unstamped documents in proceedings. When a document produced, seized, or received in proceedings under the Act is tendered by the prosecution, the court shall, unless the contrary is proved, presume the truth of its contents and the authenticity of any signature or handwriting attributed to a person, including execution or attestation. The court shall admit the document in evidence if otherwise admissible, notwithstanding that it is not duly stamped.