Return filing obligation: failure to file may trigger assessment and attract interest and penalty under tax law. Notice under Section 46 requires registered taxpayers who have not filed periodic, final (on cancellation), or annual returns to furnish the outstanding return within 15 days; failing which tax liability may be assessed based on available or gathered material, with applicable interest and penalty. The notice is system generated, does not require signature, and will be withdrawn if the taxpayer files the return before the assessment order or penalty show-cause notice is issued.