I’ve found this solution which triggers an email alert when an article is viewed, but wondered if a similar technique is possible for when a specific file is downloaded?

function article_email_alert() {
global $post;
if( $post->ID == 1234) { 
        wp_mail( 'sam@example.net', 'Alert', 'The article was visited.' );
    }
} 
add_action( 'wp', 'article_email_alert' );