XML Deserialization (DOCTYPE Issue)

Question

I am trying to Deserialize the XML input which i get. I have Created Classes for Deserialization. In my XML input there is a DOCTYPE tag which specifies the DTD.

So the problem is, if i remove the DTD tag from the input (using substring) it gets Deserialized but if i dont remove it it gets stuck at

requestObject = (Request)serializer.Deserialize(readerForDeserialization);