Using iTextSharp to create a TextField on an existing PDF

main.cs

using iTextSharp.text;
using iTextSharp.text.pdf;
  
private static void Main(string[] args)
{
  const string templateFilename = "template.pdf";
  const string outputFilename = "output.pdf";

  using (Stream inputPdf = new FileStream(templateFilename, FileMode.Open, FileAccess.Read, FileShare.Read))
  {
    using (Stream outputPdf = new FileStream(outputFilename, FileMode.Create, FileAccess.Write, FileShare.None))
    {
      var reader = new PdfReader(inputPdf);
      var stamper = new PdfStamper(reader, outputPdf);
      
      // Create a BaseFont representation of an internal font - Helvetica, 
      // using the Latin code page for Windows
      var bf = BaseFont.CreateFont(BaseFont.HELVETICA, BaseFont.CP1252, false);
      
      // This field will appear near the bottom left of the page (based on the Rectangle)
      var tf = new TextField(stamper.Writer, new Rectangle(10, 10, 154, 28), "newTextField")
      {
        Alignment = Element.ALIGN_CENTER & Element.ALIGN_MIDDLE,
        BackgroundColor = GrayColor.GRAYBLACK,
        BorderColor = Color.GREEN,
        BorderStyle = PdfBorderDictionary.STYLE_SOLID,
        DefaultText = "This is a new text field.",
        Font = bf,
        FontSize = 7,
        MaxCharacterLength = 25,
        Options = TextField.REQUIRED | TextField.MULTILINE,
        // The rotation only affects the text in the field, not the field location
        Rotation = 90,
        Text = "This is the assigned value."
      };

      // Add the TextField to the PDF on page 1
      var pageNumber = 1;
      stamper.AddAnnotation(tf.GetTextField(), pageNumber);

      // Save the changes to file
      stamper.Close();
    }
  }
}

Thank you so much man. This helped me out a ton