Hi Nicolas.
Thank you for the response.
Greek characters appear with 'dejavusans' fonts. However, the footer does not take into account that font, so I added the font-family into the .footer css style of invoice.php.
I also have done a correction in the code where the totals are caclulated :
If the item prices are with taxes included, the subtotal does not include the taxes.
Therefore, I changed line 177 ( echo $currencyHelper->format($order->order_subtotal_no_vat,$order->order_currency_id); ) with the following one :
echo $currencyHelper->format($order->order_subtotal,$order->order_currency_id);
Regards