传入文件并将其转换为byte[]

例子： string fileUrl = "C:/Users/Administrator/Downloads/233333.xls";
            FileStream fs = new FileStream(fileUrl, FileMode.Open, FileAccess.Read);
            byte[] file = new byte[fs.Length];
            fs.Read(file, 0, (int)fs.Length);
            fs.Close();
            fs.Dispose();