Hi,

You have to use XmlTextReader and XmlTextWriter：

using (FileStream fs = new FileStream("xx.xml",FileMode.OpenOrCreate))
{
XslCompiledTransform x = new XslCompiledTransform();
x.Load("xx.xslt");
XmlTextReader xreader = new XmlTextReader(fs);
XmlTextWriter xwriter = new XmlTextWriter("c:\\yyy.xml",Encoding.UTF8);
x.Transform(xreader, xwriter);
xwriter.Close();
xreader.Close();
}