Hi Enrique,
Unfortunately, as far as I know, Odoo has not yet implemented this feature in the standard version (Odoo 18) - in the sales app this is already available with the Quotation Builder, where you can add individual PDFs as an addendum or supplement to your products as additional pages.
You only have the option to set a default value for the terms and conditions in the settings of the accounting app in the ‘Customer invoices’ section, which is then displayed on all invoices by default - but unfortunately directly below the products and not on a separate page
Regards,
Chris Dominiak (Intero Technologies GmbH)