You can't do that.
All you can do is write content of the file to Response with correct MIME type in header (for example "text/plain") and client browser will open text data with configured viewer for provided MIME type.
<%@ Page language="vb" runat="server" explicit="true" strict="true" %>
2 <script language="vb" runat="server">
3 Sub Page_Load(Sender As Object, E As EventArgs)
4 Dim strRequest As String = Request.QueryString("file") '-- if something was passed to the file querystring
5 If strRequest <> "" Then 'get absolute path of the file
6 Dim path As String = Server.MapPath(strRequest) 'get file object as FileInfo
7 Dim file As System.IO.FileInfo = New System.IO.FileInfo(path) '-- if the file exists on the server
8 If file.Exists Then 'set appropriate headers
9 Response.Clear()
10 Response.AddHeader("Content-Disposition", "attachment; filename=" & file.Name) ' comment this line if needed
11 Response.AddHeader("Content-Length", file.Length.ToString())
12 Response.ContentType = "application/octet-stream" 'this is MIME type
13 Response.WriteFile(file.FullName)
14 Response.End 'if file does not exist
15 Else
16 Response.Write("This file does not exist.")
17 End If 'nothing in the URL as HTTP GET
18 Else
19 Response.Write("Please provide a file to download.")
20 End If
21 End Sub
22 </script>
http://www.xefteri.com/articles/show.cfm?id=8
Here is slightly modified c# sample code
<%@ Page Title="Home Page" Language="C#" AutoEventWireup="true"%>
<script language="cs" runat="server">
public void Page_Load(object sender, EventArgs e)
{
byte[] buffer;
using (var memoryStream = new System.IO.MemoryStream())
{
buffer = Encoding.Default.GetBytes("Hello StackOverflow"); //Dummy data
memoryStream.Write(buffer, 0, buffer.Length);
Response.Clear();
Response.AddHeader("Content-Disposition", "attachment; filename=hello.txt"); //This wil force browser to silently download file. you can comment this line to see difference
Response.AddHeader("Content-Length", memoryStream.Length.ToString());
Response.ContentType = "text/plain"; //This is MIME type
memoryStream.WriteTo(Response.OutputStream);
}
Response.End();
}
</script>