How to read pdf fields using Java?

Question

How to read pdf fields using Java?

I have a requirement when the user will fill in many fields (text box, check box, radio button) in pdf format, and they will send us by mail. I need to read all fields in pdf form and paste into oracle table.

Edit1: I am trying to use the following code. It generates a PDF, but when I double-click it, it says “invalid format”. What's wrong?

import java.io.FileOutputStream;
import java.io.IOException;

import com.itextpdf.text.*;
import com.itextpdf.text.pdf.PdfWriter;

public class pdfGentest{
    public static void main(String[] args) {

        Document document = new Document();

        try {

            PdfWriter.getInstance(document, new FileOutputStream("c:\\HelloWorld.pdf"));
            document.open();
            document.add(new Paragraph("Hello World"));
            }
        catch (DocumentException de) {
            System.err.println(de.getMessage());
            } catch (IOException ioe) {
                System.err.println(ioe.getMessage());
            }       
    }
}