How do I add a custom font to Tcpdf?

// Add more files if the font offers for // Bold styles, Oblique etc.

$pathTTFFiles = array('calibri.ttf','calibrib.ttf','calibrii.ttf','calibriz.ttf');

foreach($pathTTFFiles as $ttfFile){
   $fontname = TCPDF_FONTS::addTTFfont($_SERVER[ 'DOCUMENT_ROOT' ] . 'tcpdf/ttf/'.$ttfFile, 'TrueTypeUnicode', '', 96);
}

$pdf->SetFont('calibri', '', 10);