Open-source PDF viewing tools out there weren't reliable enough at the time. Something simple yet fully functional was needed.
Google Docs Viewer was found to be a reliable option. It isn't open-source, but still one of the best options out there as an in-browser document viewer. Simple Google Docs Viewer was created to supply the said demand.
As a result the users on the client's site (and over 1,000 sites) were able to easily view and interact with published documents. The plugin also supports responsive views, which is a great added bonus.