Modify and save existing word document using Microsoft Office Interop library in C#

Hi! Why its not worked ?

How to save word file after modify and run it

File cashdocrep.docx contain:

Pay:#Pr

Number:#n

Name:#nm

Birthday:#brth

            object fileName = @"D:\cashdocrep.docx";
            Word.Application word = new Word.Application();
            Word.Document doc = new Word.Document();
            object missing = System.Type.Missing;
            try
            {
                doc = word.Documents.Open(ref fileName, ref missing, ref missing, ref missing, ref missing, ref missing, ref missing,
                   ref missing, ref missing, ref missing, ref missing, ref missing, ref missing, ref missing, ref missing, ref missing);
                doc.Activate();
                foreach (Microsoft.Office.Interop.Word.Range docRange in doc.Words)
                {
                    if (docRange.Text.Trim() == "#")
                    {
                        docRange.Text = docRange.Text.Replace("#", "");
                    }
                    else if (docRange.Text.Trim() == "Pr")
                    {
                        docRange.Text = docRange.Text.Replace("Pr", "5.0");
                    }
                    else if (docRange.Text.Trim() == "n")
                    {
                        docRange.Text = docRange.Text.Replace("n", "0001");
                    }
                    else if (docRange.Text.Trim() == "nm")
                    {
                        docRange.Text = docRange.Text.Replace("nm", "Rustam");
                    }
                    else if (docRange.Text.Trim() == "brth")
                    {
                        docRange.Text = docRange.Text.Replace("brth", "22.12.1987");
                    }
                }
                string filePath = @"C:\cashdirection.docx";
                  if (File.Exists(filePath))
                     {
                         File.Delete(filePath);
                     }
                doc.SaveAs(filePath , missing, missing, missing, missing, missing, missing, missing, missing, missing, missing, missing, missing, missing, missing, missing);
                Process.Start("WINWORD.EXE", "\"" + filePath + "\"");
            }
            catch { }
            finally
            {
                doc.Close(ref missing, ref missing, ref missing);
                ((Word._Application)word).Quit();
            } 

Output file cashdirection.docx contain:

Pay:5.0

Number:0001

Name:Rustam

Birthday:22.12.1987