What exactly is your question? The mechanism to adapt and customize reports in Odoo did not change fundamentally from version 9 to 10. Applying Yenthe's tutorial to Odoo 10 reports should show you the way perfectly, see http://www.odoo.yenthevg.com/inheriting-and-modifying-qweb-reports/

Hello,

I am using Odoo Online version.

How can we add new fields in the invoice document? I know that it is possible to add new fields with Odoo Studio.

For example, I want to add total weight of the products in the footer. How to do that?

 Go to Settings - User Interface - Views - search "external". The views that modify the invoice template (and bills and all documents that you generate) are external_layout_footer (whose external ID is report.external_layout_footer) and external_layout_header.

Try  Clever Multiple Invoice Templates app. It will will assist you to maintain your invoices in a good way. You can manipulate it as per your requirement. You can also set different templates for different customers.  https://www.odoo.com/apps/modules/11.0/biztech_report_template/

Grettings. Please, How i can disable el field of invoice number ? I want not print the number invoice from odoo, this number come preprint in the paper. I am using odoo V10 community.