I have problems with PDF file

When attached a PDF file in the form of gravity forms, and show the entries of this form on my site (with your excellent plugin) show me a PDF file icon. By clicking the mouse on the icon always opens a lightbox window (showing strange characters without the PDF file), I want that display the file in a new window. I’ve tried everything in the configuration without success. How can i that clicking with my mouse icon open content in new window?. Thanks for your prompt help.

http://wordpress.org/plugins/gravity-forms-addons/