According to the source of pre-tax deduction vouchers, the "Measures for the Administration of pre-tax deduction vouchers of Enterprise Income Tax" will be divided into internal vouchers and external vouchers. Internal certificate refers to the original accounting certificate prepared by the enterprise for accounting expenditure when expenditure is incurred in accordance with the relevant provisions of national accounting laws and regulations. For example, the enterprise pays the salary to the employee, payroll and other accounting documents are internal documents. External certificates refer to the invoices, financial bills, tax payment vouchers, division slips and payment vouchers issued by other units and individuals obtained by enterprises when business activities and other matters occur. Among them, invoices include paper invoices and electronic invoices, and also include invoices issued by tax authorities.