How can I unload xps file in document viewer

Question

I have a word doc/rtf file and got some code that it will convert to it xps doc and It can be loaded in the DocumentViewer, I have a button that will open the file in ms word so it can be edited and saved. The problem is since the xps file is open in documentviewer, I was not able to reload the xps document in document viewer. Can some help me unloading file in document viewer. Below is my code.

private XpsDocument ConvertWordDocToXPSDoc(string wordDocName, string xpsDocName) {
 // Create a WordApplication and add Document to it
 Microsoft.Office.Interop.Word.Application
 wordApplication = new Microsoft.Office.Interop.Word.Application();
 wordApplication.Documents.Add(wordDocName);
 Document doc = wordApplication.ActiveDocument;
 try {
  doc.SaveAs(xpsDocName, WdSaveFormat.wdFormatXPS);
  wordApplication.Quit();
  XpsDocument xpsDoc = new XpsDocument(xpsDocName, FileAccess.ReadWrite);
  return xpsDoc;
 } catch (Exception exp) {
  string str = exp.Message;
 }
 return null;
}
private void LoadMyreminder() {
 string XPSMyReminder = String.Concat(Path.GetDirectoryName(_myReminder), "\\",
  Path.GetFileNameWithoutExtension(_myReminder), ".xps");
 myRemviewer.Document = ConvertWordDocToXPSDoc(
  _myReminder,
  XPSMyReminder).GetFixedDocumentSequence();
}
private void BtnEditMyrem_Click(object sender, RoutedEventArgs e) {
 Microsoft.Office.Interop.Word.Application ap = new Microsoft.Office.Interop.Word.Application {
  Visible = true
 };
 Document document = ap.Documents.Open(_myReminder);
}