Convert to PDF with php

I have the following problem, I have these value in html with php (will get the values to mysql):

Andmygoalwouldbethroughtheuseofmaterializebuttonsgavetheusertheabilitytomakescreenshotorconvertthesevaluesintopdfforlaterprinting.

I'vebeenlookingforandthoughtthebestwouldbetousethepdftoconvertdompdf.Here'sthecodeI'vegot:

<?phpuseDompdf\Dompdf;//includeautoloaderrequire_once'dompdf/autoload.inc.php';//criaraintancia$dompdf=newDOMPDF();$dompdf->load_html('<h1>Nãoseicomometeraquiosvalores</h1>');//renderizar$dompdf->render();//exibirpagina$dompdf->stream("relatorio_pii.pdf",
    array(
      "Attachment"=> false 
    )
  )
?>

And now the code for my buttons:

<div class="fixed-action-btn click-to-toggle">
      <a class="btn-floating btn-large red">
        <i class="material-icons">menu</i>
      </a>
      <ul>
        <li><a class="btn-floating red"><i class="material-icons">save</i><input type="submit" name="submitpdf" value="Download pdf file" class="input-button"/></a></li>
        <li><a class="btn-floating yellow darken-1"><i class="material-icons">camera_alt</i></a></li>
        <li><a class="btn-floating blue"><i class="material-icons">show_chart</i></a></li>
      </ul>
    </div>

The problem is that I do not know where to put the php formula to print and call the print button. Please, thank you very much for your help.