many customers ask for proforma for making advance payment.Estimate template is no good for this.What I do is make an invoice with a different set of serial numbers abbreviated PRO/INV/2021/xxx make a pdf print and correct the header to read as proforma Invoice.After sending make the invoice void ! By including PRO in search all such invoice can be grouped.Actually there is no difference between an Invoice & Proforma Invoice but for the control number and the header and may be due days for making payment..