I added the font calibri.fft,calibrii.fft, and calibrib.fft but error still exist.
pdf.add_font('Calibri','','Calibri.ttf',uni=True)
pdf.add_font('Calibri I','','Calibrii.ttf',uni=True)
pdf.add_font('Calibri B','','Calibrib.ttf',uni=True)
Underline works fine.