lopezatienza.es

System.IO.FileStream FS;

System.IO.StreamWriter SW;

string Fichero = Application.StartupPath + @"\Fichero.txt";

FS = new System.IO.FileStream(Fichero, System.IO.FileMode.Append, System.IO.FileAccess.Write);

SW = new System.IO.StreamWriter(FS);

SW.WriteLine("Texto que deseamos introducir");

SW.Close();