add_shortcode("pdf", "test_process_shortcode");

function test_process_shortcode($atts){
    $a = shortcode_atts(array('id'=>'-1'), $atts);
    // No ID value
    if(strcmp($a['id'], '-1') == 0){
        return "";
    }
    $pdf=$a['id'];
    $url=plugin_dir_url(__FILE__)."output/".$pdf."/".$pdf."/index.html";
    $iframe = "<iframe allowfullscreen class='idrws_pdf_short' src='".$url."' style='width:80%; height:800px;'></iframe>";

    return $iframe;
}