如何把excel文件導入到richtextbox中。

Question

如何把excel文件導入到richtextbox中？
  private void OpenExecl()
        {
            Microsoft.Office.Interop.Excel.ApplicationClass appWord = new Microsoft.Office.Interop.Excel.ApplicationClass();
            Type wordType = appWord.GetType();
            Microsoft.Office.Interop.Excel.Workbook execlBook;
            //Type docType = execlBook.GetType();            OpenFileDialog openFileDlg = new OpenFileDialog();
            openFileDlg.Filter = "所有文檔(*.xls,*.xlsx,*.txt,*.rtf)|*.xls;*.xlsx;*.txt;*.rtf";
            openFileDlg.Title = "选择文檔";            Bitmap bmp;
            if (openFileDlg.ShowDialog() == DialogResult.OK)
            {
               string fileName = openFileDlg.FileName;
                object readOnly = false;
                object isVisible = true;
                object missing = System.Reflection.Missing.Value;
                if (null == fileName)
                    return;
                try
                {
                    execlBook = appWord.Workbooks.Open(fileName, missing, missing, missing, missing, missing, missing, missing, missing, missing, missing, missing, missing,missing,missing);
                    int exbCount = execlBook.Worksheets.Count;
                    //for (int i = 1; i < exbCount; i++)
                    //{
                    //    Microsoft.Office.Interop.Excel.Worksheet thisSheet = (Microsoft.Office.Interop.Excel.Worksheet)execlBook.Sheets[i];
                        rhtBoxInventory.Text = execlBook.ActiveSheet.ToString();
                    //}
                }
                catch (Exception ex)
                {
                    MessageBox.Show(ex.ToString());
                }
            }
        }在try里面該怎么寫呢，一直找不到合適的方法，內容顯示不出來？
還有如何把pdf檔也讀入到richtextbox中呢？謝謝