Conditionally attach files to WooCommerce order email - Attach a file to the WooCommerce Order Completed email if a specific product or variation is in the order. https://www.damiencarbery.com/2020/02/conditionally-attach-files-to-woocommerce-order-email/

attach-files-to-wc-order-email.php

<?php
/*
Plugin Name: Conditionally attach files to WooCommerce order email
Plugin URI: https://www.damiencarbery.com/2020/02/conditionally-attach-files-to-woocommerce-order-email/
Description: Attach a file to the WooCommerce Order Completed email if a specific product or variation is in the order.
Author: Damien Carbery
Author URI: https://www.damiencarbery.com
Version: 0.1
*/


add_filter( 'woocommerce_email_attachments', 'dcwd_conditionally_attach_files_to_order_email', 10, 4 );
function dcwd_conditionally_attach_files_to_order_email( $attachments, $email_id, $object, $email_obj ) {
	// Only attach files to Completed Order email, otherwise return early.
	if ( 'customer_completed_order' != $email_id ) {
		return $attachments;
	}

	
	$upload_dir = wp_get_upload_dir();

	// Retrieve items in the order and examine each one.
	$items = $object->get_items();
	foreach ( $items as $item_id => $item ) {
		$product = $item->get_product();

		switch ( $product->get_id() ) {
			// Belt (ID 27)
			case 27: $attachments[] = $upload_dir[ 'basedir' ] . '/2018/03/belt.jpg';
					 break;
			// Long Sleeve Tee, Medium, Blue (variation ID 63)
			case 63: $attachments[] = $upload_dir[ 'basedir' ] . '/2018/03/long-sleeve-tee.jpg';
					 break;
			// A third attachment option (ID 71)
			case 71: $attachments[] = $upload_dir[ 'basedir' ] . '/2021/12/third-attachment.jpg';
					 break;
			// Two attachments: Front and back views of a t-shirt (ID 84)
			case 84: $attachments[] = $upload_dir[ 'basedir' ] . '/2021/21/t-shirt-front.jpg';
				 $attachments[] = $upload_dir[ 'basedir' ] . '/2021/21/t-shirt-back.jpg';
					 break;
		}
	}
	return $attachments;
}

Hi!
How do I add a third product to this code?
Tx!
Celine

@Celinevanc : Duplicate the block of 3 lines (comment, case, break).
I have updated the code to add a 3rd attachment option and code to add 2 attachments for a particular product.

thank you Damien, it works!