All four are trading documents with differences in who issues them and which stage they are used in: - IQ Inquiry: Buyer inquires pricing from seller. Located in left sidebar [Inquiry]. - QT Quotation: Seller's quotation to buyer. Located in left sidebar [Quotation Management]. - PO Purchase Order: Buyer's order to seller. Located in left sidebar [PO]. - PI Proforma Invoice: Seller's order confirmation and billing basis. Online payments are also processed through PI. Located in left sidebar [Proforma Invoice (PI)]. Common workflow is inquiry → quotation → buyer issues PO → seller issues PI. When you receive a customer's PO, you can click [Convert to Proforma Invoice] on that document to directly create your PI. Inquiry, quotation, and PO are not linked together. Each document type has two lists: "Sent" (documents you issued) and "Received" (documents the other party issued). Both parties have their own copy. Editing your copy does not directly change the other party's; they only see the latest version when you click [Send].