The OpenViewerFX is the successor of the open source JPedal PDF Viewer. It still uses the old jpadal code as a base but the GUI part was rewritten in JavaFX. (The project is sometimes also referred to as JavaFX PDF Viewer)
OpenViewerFX is an open source JavaFX PDF viewer. It is licensed under LGPL license and is purely written in Java which makes it a cross-platform PDF Reader/Viewer. It can be integrated into an existing Java application or can be used as a standalone application.
More information and the source code is available on github.