Presumption as to documents: handwriting, admissibility, and truth of contents govern evidentiary treatment in proceedings under the Act. Where a document is produced, seized, or received from abroad in investigations under the Act and tendered in proceedings, the authority shall presume the handwriting and signatures to be those they purport to be unless disproved, admit the document notwithstanding lack of proper stamping if otherwise admissible, and, for documents produced or seized domestically, also presume the truth of their contents unless the contrary is proved; foreign documents require prescribed authentication.