How to set landscape orientation using HTML2PDF

Using L as the constructor parameter should work just fine. Don't mess with the class internals.

This is my only code and it works fine. Try using the newest release: HTML2PDF.

// convert to PDF
require_once('../../vendor/html2pdf_v4.03/html2pdf.class.php');
try
{
    $html2pdf = new HTML2PDF('L', 'A4', 'en');
    $html2pdf->setDefaultFont('Arial');
    $html2pdf->writeHTML($html, false);
    $html2pdf->Output('output.pdf', 'D');
}
catch(HTML2PDF_exception $e) {
    echo $e;
    exit;
}

Or you can add orientation on tag.

<page orientation="landscape" format="A5" > Landscape </page>

Check out http://demo.html2pdf.fr/examples/pdf/exemple04.pdf for more example.