A factura proforma is a commercial document that previews what an invoice will look like (items, amounts, VAT) before the deal is closed, but it has no tax validity: it is not booked, not reported, and gives no right to deduct anything. The classic mistake is collecting payment against the proforma and never issuing the real invoice: the money arrives, but with no invoice behind it and no VAT reported.
Proformas are used for formal quotes, advance payments or customs procedures. If you collect an advance, you must issue an invoice for that payment at that moment, VAT included; it also helps to label the proforma clearly as such and keep it outside the numbering of your invoice series, so nobody mistakes it for a real invoice.
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