HI  Leonides Valverde Vasquez, 

This way you can achieve this ,

• First of all you have to inherit field into account.move object so create .py file  

And import this file into your _init_.py file  of models.

.py file

from odoo import fields, models,api,_

class Invoice_Account(models.Model):

    _inherit = 'account.move'

    custom_field_name= fields.Char(string=’demo’)

Xml file

• Now create report template xml file for inheriting this field into report of invoice
• Create a report template xml file and give a path to this file into your manifest file.

• You can add your custom field at any place in the invoice report by giving xpath like above pic.
• So here this way , you can add custom fields into the invoice report.

 I hope this is helpful to you.

 Thanks & Regards,

 Email: odoo@devintellecs.com

 Skype: devintelle