ช่วยด้วยครับ งมมาหลายวันแล้ว XPDF รับค่าจากตัวแปรไมไ่ด้ครับ

<?php

function expandDirectories($base_dir) 
{
      $directories = array();
      foreach(scandir($base_dir) as $file) 
      {
            if($file == '.' || $file == '..') continue;
            $dir = $base_dir.DIRECTORY_SEPARATOR.$file;
            if(is_dir($dir)) 
            {
                $directories [] = $dir;
                $directories = array_merge($directories, expandDirectories($dir));
            }elseif (end(explode(".",end(explode("/",$dir)))) == 'pdf')
            {
			 
			      $filename = explode(".",end(explode("/",$dir)))[0];            
                        $dirname = "PDF/test.pdf" . $filename . ".pdf";
                        try
                        {          
                              $command = "pdftotext -enc UTF-8 -nopgbrk " .str_replace(" ", "\ ",  $dir) . " pdftotxt/" . $filename . ".txt";
                              echo $command . "\n";
                              shell_exec($command);

                        }catch (Exception $e)                        
                        {
                              echo "error \n";
                        }  
            }
      }
      return $directories;
}

$directories = expandDirectories(dirname(__FILE__));

?>

เอาไปใช้ยังไงครับ พอผมรันหน้านี้แล้วมัน error ครับ
Notice: Only variables should be passed by reference in C:\xampp\htdocs\know_how\pdt_to text.php on line 14

Notice: Only variables should be passed by reference in C:\xampp\htdocs\know_how\pdt_to text.php on line 17
pdftotext -enc UTF-8 -nopgbrk C:\xampp\htdocs\know_how\PdfToText\examples\image-extraction\sample.pdf pdftotxt/C:\xampp\htdocs\know_how\PdfToText\examples\image-extraction\sample.txt

<?php
include('PdfToText/PdfToText.phpclass');
    $pdf = new PdfToText ('123.pdf');
    $string = "กา";
    $data = ( $pdf -> Text ) ;
   // echo $data; exit();
    if (strpos($data, $string) !== false) {
        echo $string;
    }else{
        echo "123";
    }
?>