I would like to know how to customize the VAT invoice generated by Shopify automatically.
Here’s the guide for VAT invoices for the EU and UK, but I can’t find any documentation to customize the PDF.
This community forum is for developers to flag issues when building apps or working with Shopify’s APIs - you’re best bet for questions like customising invoices would be to ask on the merchant forums here: https://community.shopify.com/
However I believe the options for customising invoices are pretty limited by default, so you might need to use an app like Sufio or Order Printer Pro: PDF Invoice to achieve what you’re looking for.
We’ve VAT complient invoice (try F: PDF Invoice) and if you wish to capture VAT ID for B2B, we support as well on cart and checkout using (try F: B2B Europe EU VAT)