C# 使用Force.com Toolkit for.NET中的ForceClient保存pdf附件

我的附件保存在lead中，但问题是它无法打开

     private string GetFileAsStringBase64(Stream stream)
        {
            var data =  new StreamReader(stream).ReadToEnd();
            var plainTextBytes = System.Text.Encoding.UTF8.GetBytes(data);
            var finalData = System.Convert.ToBase64String(plainTextBytes);
            var response = await client.CreateAsync("Attachment", new Attachment { Body = finalData , Name = _model.DirectorInformation.Attachment.FileName, ParentId = _model.LeadId });
        }
  public class Attachment
    {
        public string Body { get; set; }
        public string Name { get; set; }
        public string ParentId { get; set; }
    }

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问题是字符串数据未正确编码为base64string。 下面的代码将它转换为salesforce期望的base64字符串

            System.IO.BinaryReader br = new System.IO.BinaryReader(stream);
            Byte[] bytes = br.ReadBytes((Int32)stream.Length);
            string base64String = Convert.ToBase64String(bytes, 0, bytes.Length);
            return base64String;