Send emails with product file attached

Hi, I sell digital downloadable products in pdf. When the user buys a product, the pdf file should be attached to the complete order email.

In the complete order email, the downloadable link works perfectly, but I want to attach the actual PDF file to the email. Not only have a link but also have the PDF file as an attachment.

Example: https://www.tangoguitarlessons.com/product/novia-provinciana/

How can I do that?