When I book on airfrance.fr I get an official invoice (with VAT numbers and so on) inside a separate e-mail. If you book over the phone, you can ask for the same. There is also the option to ask retroactively for an invoice on AF website if you have purchased the ticket through them. It takes some times but works perfectly, even for FB tickets (but takes much more time because the have to ask FB).

On KL that is different : they send you the e-ticket confirmation as an invoice.