Add an attachment to emails
You can add a file attachment to your emails by adding the following code to your theme’s functions.php file:
Set the email you want the attachment to be included in, and add the path to your file. You can find the path from WP Admin → Tools → Site Health → Info → Directories and Sizes → WordPress directory location.
Upload your file to WP Admin → Media, grab the URL and replace the beginning of the URL with the path.
