Attach a pdf file (e.g. invoice) to a fulfilled email

Site URL: https://alessandradironza.com

Hi,

I'm developing a Shop Page with my prints.

I was wondering if there's a way to attach a pdf file (in my case, the invoice of the product I've sold, so it's a file which is different for every customer of course) when marking an order "Fulfilled" from Pending.

I've tried to add an html "download file" code to the Fulfilled Email HTML box, but of course you can insert only one download link, which is not what I need for the orders.

Thanks in advance for your help