MemoryStream memoryStream = new MemoryStream();
htmlDocument.Save(memoryStream); //Save Document to memory
memoryStream.Seek(0, SeekOrigin.Begin); //注意一定要seek到开头去，不然给StreamReader也是空的
StreamReader streamReader = new StreamReader(memoryStream);
C# MemoryStream -> StreamReader
原文：https://www.cnblogs.com/jt168/p/13215418.html