How to write UTF-8 text into PDF?

[Tan YuQiang]

I can write free text annotation with UTF-8 string  successfully, but when i 
use  PDPageContentStream  to draw UTF-8 string,  it is not written correctly.  
why?
My code is like below:
        PDFont font = PDType1Font.TIMES_ROMAN; 
        contentStream.setFont(font, fontSize ); //PDPageContentStream
         contentStream.moveTextPositionByAmount(x, y);
         contentStream.drawString(info.getText());

Thank you for any hint,
Devin Tan