public static void Priview(System.Web.UI.Page p, string inFilePath, string outDirPath = "")
 {
 Microsoft.Office.Interop.Excel.Application excel = null;
 Microsoft.Office.Interop.Excel.Workbook xls = null;
 excel = new Microsoft.Office.Interop.Excel.Application();
 object missing = Type.Missing;
 object trueObject = true;
 excel.Visible = false;
 excel.DisplayAlerts = false;
 string randomName = DateTime.Now.Ticks.ToString(); //output fileName
 xls = excel.Workbooks.Open(inFilePath, missing, trueObject, missing,
     missing, missing, missing, missing, missing, missing, missing, missing,
     missing, missing, missing);
 //Save Excel to Html
 object format = Microsoft.Office.Interop.Excel.XlFileFormat.xlHtml;
 Workbook wsCurrent = xls;//(Workbook)wsEnumerator.Current;
 String outputFile = outDirPath + randomName + ".html";
 wsCurrent.SaveAs(outputFile, format, missing, missing, missing,
    missing, XlSaveAsAccessMode.xlNoChange, missing,
    missing, missing, missing, missing);
 excel.Quit();
 //Open generated Html
 Process process = new Process();
 process.StartInfo.UseShellExecute = true;
 process.StartInfo.FileName = outputFile;
 process.Start();
 } 

public static void Priview(System.Web.UI.Page p, string inFilePath)
 {
 p.Response.ContentType = "Application/pdf";
 string fileName = inFilePath.Substring(inFilePath.LastIndexOf('\\') + 1);
 p.Response.AddHeader("content-disposition", "filename=" + fileName);
 p.Response.WriteFile(inFilePath);
 p.Response.End();
 }

 public static void Preview(System.Web.UI.Page p, string inFilePath)
 {
 string fileName = inFilePath.Substring(inFilePath.LastIndexOf('\\') + 1);
 p.Response.ContentType = "text/plain";
 p.Response.ContentEncoding = System.Text.Encoding.UTF8; //保持和文件的編碼格式一致
 p.Response.AddHeader("content-disposition", "filename=" + fileName);
 p.Response.WriteFile(inFilePath);
 p.Response.End();
 }