.NET : How to validate XML file with DTD without DOCTYPE declaration

I have an XML file with no DOCTYPE declaration that I would like to validate with an external DTD upon reading.

Dim x_set As Xml.XmlReaderSettings = New Xml.XmlReaderSettings()
x_set.XmlResolver = Nothing
x_set.CheckCharacters = False
x_set.ProhibitDtd = False
x = XmlTextReader.Create(sChemin, x_set)

How do you set the path for that external DTD? How do you validate?

From stackoverflow

• Could you create an Xml.XmlDocument with the DTD you want, then append the XML file data to the in-memory Xml.XmlDocument, then validate that?

• I have used the following function successfully before, which should be easy to adapt. How ever this relies on creating a XmlDocument as magnifico mentioned. This can be achieved by:

  XmlDocument doc = new XmlDocument();
  doc.Load( filename );
  doc.InsertBefore( doc.CreateDocumentType( "doc_type_name", null, DtdFilePath, null ), 
   doc.DocumentElement );
  
  
  /// <summary>
  /// Class to test a document against DTD
  /// </summary>
  /// <param name="doc">XML The document to validate</param>
  private static bool ValidateDoc( XmlDocument doc )
  {
   bool isXmlValid = true;
   StringBuilder xmlValMsg = new StringBuilder();
  
   StringWriter sw = new StringWriter();
   doc.Save( sw );
   doc.Save( TestFilename );
  
   XmlReaderSettings settings = new XmlReaderSettings();
   settings.ProhibitDtd = false;
   settings.ValidationType = ValidationType.DTD;
   settings.ValidationFlags = XmlSchemaValidationFlags.ReportValidationWarnings;
   settings.ValidationEventHandler += new ValidationEventHandler( delegate( object sender, ValidationEventArgs args )
   {
    isXmlValid = false;
    xmlValMsg.AppendLine( args.Message );
   } );
  
   XmlReader validator = XmlReader.Create( new StringReader( sw.ToString() ), settings );
  
   while( validator.Read() )
   {
   }
   validator.Close();
  
   string message = xmlValMsg.ToString();
   return isXmlValid;
  }