Legal analysis: it is not illegal, and the stamp of the invoice on the receipt has no legal effect, which is clearly stipulated by our laws. Invoices are special, and receipts cannot be used as invoices.

Legal basis: Article 28 of the Detailed Rules for the Implementation of the Measures for the Administration of Invoices in People's Republic of China (PRC) stipulates that when issuing invoices, units and individuals must fill in the invoices in numerical order, and the items filled in are complete, so as to ensure that the contents are true and legible, and all of them are printed at one time, and the contents are completely consistent, and the invoice seal is affixed to the invoice joint and the deduction joint.