Need help/suggestion to build PDF form filling program

Hello,

I am having a PDF Viewer written in Java, it is based on JPedal.
Now I want to have the program an ability to fill forms in the PDF, I started by testing an example come from JPedal, it is the SimpleViewer class. It allows me to type text into fields but when I try to re-save the form, nothing happens. No error logged.

I would like to ask for suggestion/advice from guys who already have experience on this.

Thanks