Invoice Report Layout on Odoo 12
I am using Odoo 12 Community edition and I choose a sample for the invoice layout, but I would like to customize it. I found in the Views > report_invoice_document, but this is not the full document, I cannot find how to modify the header and the footer. I tried looking for external_layout_header and external_layout_footer as I read on some other places, but it doesn't exist. Can someone explain to me how could I find out which views are used in the current settings?
Another question would be if there is any external tool to edit and create these Reports and then import them back into Odoo.
Thanks for your help, I appreciate it.