PdfStamper is not being executed in C# WinForms

I've this piece of code bellow, but when it reaches to PdfStamper it stops the code, and leaves, giving nothing, not even an error.

What could be the solution for this problem?

    private void FillForm()
    {
        try
        {
            string pdfTemplate = @"C:\Users\Diogo\Desktop\files\IMTT.pdf";
            string newFile = @"C:\Users\Diogo\Desktop\P.pdf";
            PdfReader pdfReader = new PdfReader(pdfTemplate);
            pdfReader.SelectPages("1");
            using (FileStream stream1 = File.Open(newFile, FileMode.OpenOrCreate))
            {
                PdfStamper pdfStamper = new PdfStamper(pdfReader, stream1); //stops here
                AcroFields pdfFormFields = pdfStamper.AcroFields;

                pdfFormFields.SetField("Nome.12", "TESTE");
                pdfStamper.FormFlattening = false;
                pdfStamper.Close();
                stream1.Close();
            }
        }
        catch (Exception msg) 
        {
            string m = msg.Message;
        }
    }