In previous versions, the PdfViewer.PopupMenuShowing event could not be raised for the context menu shown in the navigation pane.
Now, the Usability - Provide the capability to raise the PdfPopupMenuShowing event when a popup menu is shown in a bookmarks tree suggestion has been implemented.
The PdfPopupMenuShowingEventArgs.Menu property has become obsolete and returns null when the PopupMenuShowing event is raised for outlines. Use the ItemLinks property instead to avoid this behavior.
You can also obtain the current popup menu type shown for the PDF Viewer using the PdfPopupMenuShowingEventArgs.PdfPopupMenuKind property. This property can return one of the PdfPopupMenuKind enumeration values: PageContent, BookmarkTree, and BookmarkOptions.