Windows form C #, write in n text file from textbox

Hello,
I have the impression to have deleted my message, I'm sorry I start again.
Three lines to edit in a text file in C #.
I have the following error message:
System.ArgumentException: 'The stream can not be written.'
How to replace lines with StreamWriter?
Thanks for your help,
Forgive my English, it's google translation ...

private void Btn_valider_tarif_Click(object sender, EventArgs e)
 {
     Stream stream = System.Reflection.Assembly.GetExecutingAssembly().GetManifestResourceStream("monappli.Resources.fichier.txt");

     string[] lines = { Txt1.text, "Txt2.text", "Text3.text" };

using (StreamWriter file_name = new StreamWriter(stream, ASCIIEncoding.Default))
     {
         foreach (string line in lines)
         {
             file_name.WriteLine(line);
         }
     }
 }