Here is a simple function to ease changing fonts in your PDF.
function pdf_font($pdf,$size,$face='arial')
{
//Set the path
$path=$_SERVER['DOCUMENT_ROOT'];
${$face} = $face."=$path/fonts/".$face.".ttf";
pdf_set_parameter($pdf, 'FontOutline',${$face});
$font=pdf_findfont($pdf,$face,"host",0);
pdf_setfont($pdf,$font,$size);
}