Invoice per Email

Hi,

So you basically want to edit the "order notification" email that you can send through the "email" button of the order details page of the backend so that you can easily send the email with your bank details to the customer.
Since you just want to add texte to that email, I would recommend to use translation overrides in order to change the text in the email:
www.hikashop.com/download/languages.html#modify
If you really want to edit the email further, that's normally done with the menu System>Emails with the Business edition so that you don't loose the changes each time you update HikaShop.
With the Essential edition, you would have to edit the mail files under the folder media/com_hikashop/mail