protected void ManipulatePdf(String dest)
{
PdfDocument pdfDoc = new PdfDocument(new PdfReader(SRC), new PdfWriter(dest));
PdfAcroForm form = PdfAcroForm.GetAcroForm(pdfDoc, true);
PdfFormField button = form.CopyField("Test");
PdfArray rect = button.GetWidgets()[0].GetRectangle();
// Increase value of the right coordinate (index 2 corresponds with right coordinate)
rect.Set(2, new PdfNumber(rect.GetAsNumber(2).FloatValue() + 172));
button.SetValue("Print Amended");
form.ReplaceField("Test", button);
pdfDoc.Close();
}