How to download file in asp.net using c#?

In this article, I will show you how to download a file using asp.net c#. Based on the file extension you can set the content type value to be get downloaded. The Response.TransmitFile retrieves file by using file server path and writes to it response.
Here the user can upload the file using file upload control and show it in a label control. When the user clicks the download button it will check whether it is text or pdf or doc or JPEG file and get downloaded as per ContentType. 

Download.aspx:

<form id="form1" runat="server">
        <div>
            <table style="padding: 20px;">
                <tr>
                   <td>
                       <asp:Label ID="lblFilename" runat="server" Text="Browse:"></asp:Label>
                   </td>
                   <td>
                       <asp:FileUpload ID="fileUpload1" runat="server" />
                   </td>
                </tr>
                <tr>
                   <td colspan="2">&nbsp;
                   </td>
                </tr>
                <tr>
                   <td>
                       <asp:LinkButton runat="server" OnClick="lnkUpload_Click" Font-Underline="False">Upload</asp:LinkButton>
                   </td>
                   <td>
                       <asp:LinkButton runat="server" OnClick="lnkDownload_Click" Font-Underline="False">Download</asp:LinkButton>
                   </td>
                </tr>
            </table>
        </div>
    </form>

Download.aspx.cs:

protected void lnkUpload_Click(object sender, EventArgs e)
    {
       filename= Path.GetFileName(fileUpload1.PostedFile.FileName);
       fileUpload1.SaveAs(Server.MapPath("Uploads/" + filename));
       Response.Write("Fileuploaded sucessfully.");
       lblFilename.Text = "Uploads/" + fileUpload1.FileName;
    }
 
    // To download uplaoded file
    protected void lnkDownload_Click(object sender, EventArgs e)
    {
        if (lblFilename.Text != string.Empty)
        {
            if (lblFilename.Text.EndsWith(".txt"))
            {
               Response.ContentType = "application/txt";
            }
            else if (lblFilename.Text.EndsWith(".pdf"))
            {
               Response.ContentType = "application/pdf";
            }
            else if (lblFilename.Text.EndsWith(".docx"))
            {
               Response.ContentType = "application/docx";
            }
            else
            {
               Response.ContentType = "image/jpg";
            }
            string filePath = lblFilename.Text;
 
           Response.AddHeader("Content-Disposition", "attachment;filename=\"" + filePath + "\"");
           Response.TransmitFile(Server.MapPath(filePath));
           Response.End();

Download file to client PC: