Visual CSharp .NET - Generar factura PDF

Document document = new Document();

PdfWriter.GetInstance(document, new FileStream("E:/Respuestas2.pdf", FileMode.OpenOrCreate));

document.Open();

document.Add(new Paragraph("Respuestas a la Encuesta"));

for (int i = 0; i < ListadoRespuestas.Count(); i++)

{

   document.Add(new Paragraph(ListadoRespuestas[i]));

}

document.Close();

string WorkingFolder = Environment.GetFolderPath(Environment.SpecialFolder.Desktop);

string InputFile = Path.Combine(WorkingFolder, "E:/Respuestas2.pdf");

string OutputFile = Path.Combine(WorkingFolder, E:/Respuestas.pdf");

using (Stream input = new FileStream(InputFile, FileMode.Open, FileAccess.Read, FileShare.Read))

{

 using (Stream output = new FileStream(OutputFile, FileMode.Create, FileAccess.Write,   FileShare.None))

{

 PdfReader reader = new PdfReader(input);

 PdfEncryptor.Encrypt(reader, output, true, txtDocumento.Text, "secret", PdfWriter.ALLOW_SCREENREADERS);

}

}

System.IO.File.Delete(@"E:/Respuestas2.pdf");