Add PDF to purchase receipt

/**

 *

 * @param  array  $attachments  required  Any existing attachments

 * @param  int    $payment_id   optional  ID of the current payment

 * @param  array  $payment_data optional  The remaining payment data

 * @return array  $attachments            Now our attachment is added

 */

function edd_add_pdf_to_purchase_receipt( $attachments, $payment_id, $purchase_data ) {

	$attachments   = array();

	$attachments[] = WP_CONTENT_DIR . '/assets/pdf/file1.pdf';

	$attachments[] = WP_CONTENT_DIR . '/assets/pdf/file2.pdf';

    return $attachments;

}

add_filter( 'edd_receipt_attachments', 'edd_add_pdf_to_purchase_receipt', 10, 3 );