Google announced via his Official Gmail Blog the support of TIFF and Powerpoint files in their Gmail application. PDF files were already supported for a while.
For a few months, PDF files have been hit by several security issues and recently, a zero-day exploit targeted Powerpoint files. Why not use GMail as a sandbox? [If you don’t know the principle of a sandbox, read my article posted a few months ago].
When I received a file from an untrusted source (can we still trust somebody today?), I send the suspicious file to my own Gmail account and open it with the integrated viewer. Files are displayed inside the browser and does not interact with the operating system. Simple and safe!