Code for viewer
<div style=”left: 0; width: 100%; height: 0; position: relative; padding-bottom: 129.4118%;”><iframe style=”top: 0; left: 0; width: 100%; height: 100%; position: absolute; border: 0;” src=”https://docs.google.com/viewer?embedded=true&url={@pdf_url}” allowfullscreen=”allowfullscreen”></iframe></div>