In some different cases it would be really usefull to create a button which calls the navigation bar from the viewer app.
I have a animation in the background, which is done as a video. The user shouldn't be able to interact with that animation in any case. If the controls are hidden, the user can still click on the video to stop it. This can be solved if you put another interactive element on top, so the video can't be stoped. For example a button which links to the same article and same page number.
BUT in this case, you can click on the animation, and nothing happens, but it would be nice to get the navigation bar.