Builds a print-ready A4 invoice from the form and the line items: seller and customer blocks, number, date and due date, an itemised table with subtotal, discount (amount or %), tax and total, the total in words (English or Indonesian), payment details, notes and an optional signature block, with a DRAFT/UNPAID/PAID stamp. Amounts accept 12.000.000, 12,000,000 or 12000000. Print the preview (or the downloaded HTML) to PDF from the browser. Everything runs locally.