What is Google Docs Viewer?
With Google Docs Viewer, you can quickly view many file types online, including PDFs, Microsoft Office files, and many image file types.
NOTE: Even if the official webpage redirects to Google Drive , Google Docs Viewer can be still used pasting the URL https://docs.google.com/viewer?url= in a new tab and then paste the address of the document you want to view online.
Focus has moved to Google Drive but Docs Viewer is still accessible: http://googlesystem.blogspot.com/2015/02/google-docs-viewer-page-no-longer.html
Google Docs Viewer Screenshots
Google Docs Viewer Features
Google Docs Viewer information