Load document byte from sql server database. save it to temporary storeage , and view in browser.

public void Download() {

string fileName = "abc.doc";
string _path = Request.PhysicalApplicationPath + "Temp/" + fileName;

byte[] filebyte = new byte[0]; // load from database

File.WriteAllBytes(_path, filebyte );

oR.showReportAjax(ResolveUrl("~/Temp/" + fileName), this.GetType(), this, UpdatePanel1);

}

public void showReportAjax(string pageUrl, Type cType, Page oPage, Control ctrl)
{
string url = ResolveClientUrl(pageUrl) ;

ScriptManager.RegisterStartupScript(ctrl, typeof(string), "redirect", "window.open('" + url + "');", true);

} 

Method 2

System.Web.HttpResponse response = System.Web.HttpContext.Current.Response;
        response.ClearContent();
        response.Clear();
        response.ContentType = "text/plain";
        response.AddHeader("Content-Disposition", 
                           "attachment; filename=" + fileName + ";");
        response.TransmitFile(Server.MapPath("FileDownload.csv"));
        response.Flush();    
        response.End();