In flexpaper I want to show next and previous page using right and left button using its API

In flexpaper I want to show next and previous page using right and left
button using its API

I am using this to button using onclick
<input type="submit" value="Invoke" onclick="getDocViewer().nextPage()">
<input type="submit" value="Invoke" onclick="getDocViewer().prevPage()">
but it throw error 'Cannot call method 'getApi' of undefined'
how do I fix this ?