phpBB - opening a .pdf attachment in new window?

Currently if I attach a .pdf to a post, clicking it starts it downloading. I’d like it to load and open for viewing. I know it’s not defaulted this way for security purposes, but the forum only has a handful of members, all personally known, it’s not an open forum.

It’s php 5.2, and I have a php.ini file I used to increase my upload sizes - -is there something in there I need to tweak to allow .pdf’s to open and be viewed?