I'm not quite sure if any changes to the invoice templte are possible. But maybe there are some ways how it can be manifested. Usually I use Adobe Acrobat, because it's easy to figure out how to use it ( at least for me). I've also ran into this site
https://pdfliner.com/ds_11_form but I still prefer to use adobe rather then this one. But you could try both. Maybe it will help you and something'll be more convenient.