<script language="javascript" type="text/javascript">
      function uploadFile() {
            document.getElementById('btnUpload').click();
      }
</script>

Step 3: Write btnUpload click event handler in the codebehind page.

protected void btnUpload_Click(object sender, EventArgs e)
{
      try
      {
            HttpFileCollection uploadFiles = Request.Files;
            for (int i = 0; i < uploadFiles.Count; i++)
            {
                  HttpPostedFile uploadFile = uploadFiles[i];
                  string fileName = Path.GetFileName(uploadFile.FileName);
                  if (fileName.Trim().Length > 0)
                  {
                        uploadFile.SaveAs(Server.MapPath("./Others/") + fileName);
                        lblStatus.Text = "File Uploaded Successfully";
                  }
            }
      }
      catch (Exception ex)
      {
            lblStatus.Text = "Error in uploading file";
      }
}

Step 4: Create another aspx page, place a updatepanel which will contain IFrame and a button. Load the FileUpload.aspx in the IFrame. uploadFile javascript method in the FileUpload.aspx will be invoked from the btnUpload button of this aspx page.

This ends the article of upload file withing upldatepanel.