An e-invoice is an invoice in a structured electronic format that software can process automatically. A PDF sent by email is not an e-invoice: it carries a picture of the invoice, not its data.
In the UAE the format is PINT AE, and from 2027 the invoice must travel through an accredited service provider rather than by email. The mandate covers B2B and B2G transactions; invoices to consumers stay outside it.
Official source: Ministry of Finance — eInvoicing