Verification of self-assessment: proper officer may require documents from importer or exporter for duty ascertainment. Subsection (3) is substituted to authorize the proper officer to require the importer, exporter or any other person to produce any document or information whereby the duty leviable on imported or export goods can be ascertained, and to oblige such persons to produce or furnish the required documents or information for verification of self-assessment under subsection (2).