using Microsoft.Win32;// opendialog

        private void OpenExecuted(object sender, ExecutedRoutedEventArgs e)
        {            
            OpenFileDialog openFileDialog1 = new OpenFileDialog();
            openFileDialog1.Filter =
               "CAD-XML Dateien (*.xml)|*.xml|Alle Dateien (*.*)|*.*";
            openFileDialog1.FilterIndex = 1;// zählt von 1 !
            openFileDialog1.DefaultExt = ".xml";
            openFileDialog1.InitialDirectory = System.Environment.CurrentDirectory;
            openFileDialog1.Multiselect = false;  // true
            openFileDialog1.RestoreDirectory = true;
            if (openFileDialog1.ShowDialog() == true)
            {
                // Verarbeitung
                string sFile = openFileDialog1.FileName;
            }
        }

        private void OpenExecuted2(object sender, ExecutedRoutedEventArgs e)
        {            
            OpenFileDialog openFileDialog1 = new OpenFileDialog();
            openFileDialog1.Filter =
               "CAD-XML Dateien (*.xml)|*.xml|Alle Dateien (*.*)|*.*";
            openFileDialog1.FilterIndex = 1;// zählt von 1 !
            openFileDialog1.DefaultExt = ".xml";
            openFileDialog1.InitialDirectory = System.Environment.CurrentDirectory;
            openFileDialog1.Multiselect = true
            openFileDialog1.RestoreDirectory = true;
            if (openFileDialog1.ShowDialog() == true)
            {
                // Verarbeitung
		foreach (string sFilename in openFileDialog1.FileNames) {
                	// ...
		}
            }
        }