C#文档转为Base64位字符串

        public static  string DocumentToBase64Str(string fileName)
        {
            FileStream filestream = new FileStream(fileName, FileMode.Open);

            byte[] bt = new byte[filestream.Length];
            //调用read读取方法
            filestream.Read(bt, 0, bt.Length);
            string base64Str = Convert.ToBase64String(bt);
            filestream.Close();
            return base64Str;
        }