Remove DTD from XML file using SSIS script Task

I have to remove DTD from 2 GB XML file , i have used below code for that , but i have getting system out of memory exception. even though there 16 GB RAM on server /



XmlDocument XDoc = new XmlDocument();
   xmlDoc.XmlResolver = null ;
                XDoc.Load(Dts.Variables["D:\\xmlfiles\\old.xml"].Value.ToString());
                XmlDocumentType XDType = XDoc.DocumentType;
                XDoc.RemoveChild(XDType);
                XDoc.Save(Dts.Variables["D:\\xmlfiles\\new.xml"].Value.ToString());

Is there other way to remove DTD, pls help on this ..