Send mail to author when custom post type is saved

Try this way:

function send_emails_on_new_event( $post ) {

    $emails="[email protected]";
    $headers="From: Name <[email protected]>";
    $title   = wp_strip_all_tags( get_the_title( $post->ID ) );
    $message="New post created";

    if ( get_post_type( $post->ID ) === 'documents' ) {
        wp_mail( $emails, 'New Post', $message, $headers );
    }
}
add_action( 'pre_post_update', 'send_emails_on_new_event' );

From the Code Reference:

pre_post_update: Fires immediately before an existing post is updated in the database.