Legal analysis: You need to sign a purchase and sale contract to open an ordinary invoice. If you need to make an ordinary invoice, you need to refer to the contents of the purchase and sale contract. The purchase and sale contract is a form of written proof. If you have bought an ordinary invoice, you need to keep the purchase and sale contract for future reference. If you need to apply to the tax bureau for invoicing, you need to review the original purchase and sale contract.

Legal basis: Article 16 of the Detailed Rules for the Implementation of the Measures for the Administration of Invoices, units and individuals that need to use invoices temporarily may directly apply to the tax authorities in the place of business for issuing invoices on the basis of written certificates of buying and selling commodities, providing or receiving services and engaging in other business activities and the identity certificate of the agent.