Error using Dompdf

I'm using dompdf to generate pdf and returns this ERROR :

  

Fatal error: Uncaught Error: Call to undefined function   Dompdf \ mb_internal_encoding () in   C: \ Users \ adnas \ logisticapratica \ logisticapratica \ php \ pdf \ dompdf \ src \ Dompdf.php   online 274

Code:

<?php
  use Dompdf\Dompdf;
  require_once 'dompdf/autoload.inc.php';

  $dompdf = new DOMPDF();

  $dompdf->load_html('<h1>gerar pdf</h1>');

  $dompdf->render();
  $dompdf->stream(
    'teste.pdf',
    array(
      "Attachment" => false
    )
  );
?>;