Allow PDF and block rest of File Types

Hi,

Is it possible to configure to block documents file types except for PDFs for downloads? E.g. users can download PDF but rest of the file types (doc, .xls, .ppt..etc..) are blocked.

I'm having difficulty setting up policy for the above requirement. We are using Web Security v7.7.3 and integrated with TMG 2010 proxy.

Is there any option to achieve this or can a regular expression will help?

Appreciate for any input.

Regards,

Jonathan