Thanks, Irosenth.
The barcode font I used is Installable. But it is not embedded.
In fact I tried adding two lines of watermarks, one using the barcode font and the other using Windows Courier font. I checked the created pdf file, both of them were not embedded.
Like I said, after I added a file using addWatermarkFromFile(), the fonts were embedded.
Also, I printed the document through the Adobe PDF printer driver, the fonts were embedded.
It looks to me that these fonts are embeddable. But they just are not embedded with the addWatermarkFromText() function.
Any further suggestions?