Hi,

To edit the Invoice PDF report, follow the steps below.

1- Settings > Technical > Reports.

2 - Search for the Invoice report. Go to the external link for the paper format of the invoice report.

3- We can edit the size of the invoice report as we need in this paper format.

By adjusting the values in each field, we can customize our invoice report size.

Hope it helps

Yes, in Odoo 18 (or any recent Odoo version), editing the invoice size (PDF layout) is possible. This usually refers to modifying the PDF invoice's page size, margins, font size, spacing, or layout elements like logos, address blocks, and tables.  This video demonstrates the configuration steps for editing the invoice size in the PDF layout. 

       https://drive.google.com/file/d/1XhZ4frJGu0XxV6M0S0HxmhaWiyBEwskp/view?usp=sharing