async void FlexViewer_NavigateToCustomTool(object sender, CustomToolEventArgs e)
 {
     if (e.Tool == FlexViewerTool.CustomTool1)
     {
         await OpenPdf();
     }
     else if (e.Tool == FlexViewerTool.CustomTool2)
     {
         _pdfDocSource.ClearContent();
     }
     else if (e.Tool == FlexViewerTool.CustomTool3)
     {
         await ChangeUseSystemRendering();
     }
 }
 void Page_Unloaded(object sender, RoutedEventArgs e)
 {
     _pdfDocSource.ClearContent();
 }
 private void FlexViewer_CloseAction(object sender, EventArgs e)
 {
     pdfDocumentSource.ClearContent();
     fv.CloseActionEnabled = false;
     fv.FocusPane();
 }