Presumption as to documents: prosecution-tendered documents are presumed genuine unless counter-evidence, and admitted if otherwise admissible. When a document produced, seized, or received from abroad in proceedings under the Act or any other law is tendered by the prosecution against the person or any jointly tried person, the court shall, unless contrary is proved, presume the truth of its contents and that any signature or handwriting is that of the person it purports to be, and that an executed or attested document was executed or attested by the person it purports; the court shall admit such a document even if not duly stamped, if otherwise admissible.