Hi Giriprasad,
1) If that's a static text you could do it at form design time.
2) If that's dynamic text and if you know which data to be in bold, send it in a separate field from your driver program, on the form instead of normal field use floating field and set that a bold considering the bold word always comes in a specific sequence etc.
3) If its entirely random pass the formatted text as an html content to form, on form present it as a richtext info on this is available in the links posted by Christopher above.
Cheers,
Sai