解决的方法

    ob_end_clean();
    header('Content-type:application/pdf');//下载的文件类型信息
    header('Content-Disposition: attachment; filename=name');
    header('Content-Length:'.filesize($file)); //内容长度
    ob_start();
    echo file_get_contents($file);
    $downloadData = ob_get_contents();
    ob_end_clean();
    echo $downloadData;