如何在TCPDF中设置多个字体

I already use my custom font in TCPDF. Now I tried to add the bold font type (also by adding the 'style' parameter), but without success:

$objPdf->SetFont('opensanscondensedlight', '', 12);
$objPdf->SetFont('opensanscondensedbold', 'B', 12);

Does anyone have an idea how to solve this?