我尝试加载文件时出现异常，无法读取超出流的末尾

Question

我尝试读取RTF文件并将其发送到Excel文件。我这样做：

Byte[] rtf;
using (FileStream stream = new FileStream(Server.MapPath("/1.RTF"), 
    FileMode.Open, FileAccess.Read))
{
    int size = Convert.ToInt32(stream.Length);
    rtf = new Byte[size];
    stream.Read(rtf, 0, size);
};

textx = System.Text.Encoding.GetEncoding("utf-8").GetString(rtf);

string file = @"C:\Users\ITS_prog\Desktop\newdoc.xls";
Workbook workbook = Workbook.Load(file);
Worksheet worksheet = workbook.Worksheets[1];
worksheet.Cells[0, 1] = new Cell((short)1);
worksheet.Cells[2, 0] = new Cell(9999999);
worksheet.Cells[3, 3] = new Cell((decimal)3.45);
worksheet.Cells[2, 2] = new Cell(textx);
worksheet.Cells[2, 4] = new Cell("Second string");
worksheet.Cells[4, 0] = new Cell(32764.5, "#,##0.00");
worksheet.Cells[5, 1] = new Cell(DateTime.Now, @"YYYY-MM-DD");
worksheet.Cells.ColumnWidth[0, 1] = 3000;
workbook.Save(file);

但在这一行中，Workbook workbook = Workbook.Load(file);我的应用提供例外：

  

异常无法读取超出流的结尾。

我做错了什么？