iTextSharp, deal with template

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itextsharp

hey everyone, im new to iTextSharp, i wanted to have a new pdf file by update the existing template pdf, and i followed this tutorial
http://simpledotnetsolutions.wordpress.com/2012/04/08/itextsharp-few-c-examples/

i have a problem with fillPDFForm()
this is my code:

public string P_InputStream = "template/test.pdf";
public string P_OutputStream = "output/test.pdf";

 public template()
 {
     InitializeComponent();
 }
 
private void template_Load(object sender, EventArgs e)
 {
     string formFile = P_InputStream;
     string newFile = P_OutputStream;
     PdfReader reader = new PdfReader(formFile);
     using (PdfStamper stamper = new PdfStamper(reader, new FileStream(newFile, FileMode.Create)))
     {
         AcroFields fields = stamper.AcroFields;

         // set form fields
         fields.SetField("customerName", "John Doe");
         fields.SetField("Address", "xxxxx, yyyy");
         fields.SetField("Test", "12345");

         // flatten form fields and close document
         stamper.FormFlattening = true;
         stamper.Close();
     }
 }

after the form load, the data inside the pdf file is still the same, din't update. perhaps i dint create the pdf file properly? this is how i did:
1. i open a open office writer
2.Insert Fields>under Variables tab>choose "Set Variable" for Type and "General for Format
3.type the name, and click Insert.
4. File>Export as PDF

am i doing this right?