As I said in the comments, try changing the font before using Cell() or Multicell() , an example follows:
$pdf=new PDF(); ... $pdf->Cell(180,10,'bla bla',0,1,'C'); $pdf->SetFont('Times','B',16); //Change to bold $pdf->Cell(180,10,'bla bla bla',0,1,'C'); //this printed in bold $pdf->SetFont('Times','',12); //Revert to plain font $pdf->Cell(180,10,'bla bla bla',0,1,'C');
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