how to save wordfile using save file dialog box

You cannot save a text file as a word document through a save dialog[^]. The dialog merely allows your user to decide the location and name of the file that your content will be saved in. You must still convert the content into the correct format and then write it into the file selected. Take a look at the Word Interop[^] library for information on creating doc/docx files.

<asp:textbox id="txtDescription" runat="server" textmode="MultiLine" height="100" xmlns:asp="#unknown">
            Width="280"></asp:textbox>
        <asp:linkbutton id="lb_Download" runat="server" text="Download file" onclick="lb_Download_Click" xmlns:asp="#unknown"></asp:linkbutton>

protected void Page_Load(object sender, EventArgs e)
    {
        if (!IsPostBack)
        {
            txtDescription.Text = "lorem Ipsum is simply dummy text of the printing and typesetting industry. Lorem Ipsum has been the industry's standard dummy text ever since the 1500s, when an unknown printer took a galley of type and scrambled it to make a type specimen book. It has survived not only five centuries, but also the leap into electronic typesetting, remaining essentially unchanged. It was popularised in the 1960s with the release of Letraset sheets containing Lorem Ipsum passages, and more recently with desktop publishing software like Aldus PageMaker including versions of Lorem Ipsum.";
        }
    }
    protected void lb_Download_Click(object sender, EventArgs e)
    {
        string strContents = null;
        strContents = txtDescription.Text;

        string attachment = "attachment; filename=test.doc";
        Response.ClearContent();
        Response.ContentType = "application/doc";
        Response.AddHeader("content-disposition", attachment);
        Response.Write(strContents);
        Response.End();
    }

object missing = System.Reflection.Missing.Value;
       object Visible = true;
       object start1 = 0;
       object end1 = 0;

       Microsoft.Office.Interop.Word.ApplicationClass WordApp = new Microsoft.Office.Interop.Word.ApplicationClass();
       Microsoft.Office.Interop.Word.Document adoc = WordApp.Documents.Add(ref missing, ref missing, ref missing, ref missing);
       Microsoft.Office.Interop.Word.Range rng = adoc.Range(ref start1, ref missing);
       SaveFileDialog saveFileDialog1 = new SaveFileDialog();
       saveFileDialog1.InitialDirectory = @"C:\";
       saveFileDialog1.Title = "Save word Files";
       saveFileDialog1.CheckFileExists = false;
       saveFileDialog1.CheckPathExists = true;
       saveFileDialog1.DefaultExt = "docx";
       saveFileDialog1.Filter = "Docx files (*.docx)|*.doc|All files (*.*)|*.*";
       saveFileDialog1.FilterIndex = 2;
       saveFileDialog1.OverwritePrompt = true;
       saveFileDialog1.RestoreDirectory = true;

       if (saveFileDialog1.ShowDialog() == DialogResult.OK)
       {
           rng.Font.Name = "Calibri (Body)";
           rng.InsertAfter(txtenglishtext.Text);
           object filename = saveFileDialog1.FileName;
           adoc.SaveAs(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);
           WordApp.Visible = true;
       }