Supports Word, Excel, PowerPoint, PDF, ZIP and more formats. File should be online and publicly accessible. Opened files can be easily saved to the Google Drive. Doesn’t work on ***Google Search Result Pages***.
List of supported file types: https://support.google.com/drive/answer/2423485?hl=en&p=docs_viewer&rd=1
Test extension on this page: http://browsernative.com/test/drive.php
Not affiliated with Google.