Beginning with Java 9, the search in pag function will not be available by default in the Help system, because it tries to make accessible a private internal field of the WebEngine.
However, by default the possible exception will not be shown, and the search by CTRL+F will simply do nothing. The HelpContentViewer.showSearchExceptions(boolean) will allow to show the exception the first time the search on a page is tried by showing a popup with the exception message[1]