When exporting to an FDF file, the user does have the option of signing the file, so yes, and FDF file may contain a digital signature.
can you give a sample that can display the digital signature in fdf file? i really that help right now...
To start with, here's a screen shot:
I've attached the FDF file to the post as well. When you go to open the file after you've downloaded it to your local machine don't forget to change the "Files of type" to All Files.
The default is PDF and you won't see the FDF file unless you reset the "Files of type" in the Open dialog.