Shortcode problem in Wordpress

function show_wpdf_dir($atts,$content = null){
    echo 'test';
}
function show_auto_pdf_dir($content){
    $postid = get_the_id();
    $check = get_post_custom_values('wp-pdf-dir', $postid);
    if(!empty($check[0]) && $check[0] !== '000000' && is_page()){
        $month = substr($check[0],0,2);
        $year = substr($check[0],2,7);
        echo $content.show_wpdf_archive($year,$month);
    } else {
        echo $content;
    }
}
add_filter('the_content', 'show_auto_pdf_dir');
add_shortcode( 'wp-pdf-dir', 'show_wpdf_dir' );