Adding different paper sizes is only available in the premium version of the plugin. Available paper sizes are A3, A4, A5, Letter, or any custom dimension.
- Go to the Woo Invoice > Settings from your WordPress Dashboard.
- Click on the Invoice tab.
- Into Invoice Template section you will find an option to select your Paper Size. If you need a custom dimension then select the option Custom Paper size and enter width and height in millimeter (mm).