How to Set Adobe Reader as your Default Application in Ubuntu 14.04 when ‘Open with’ doesn’t Work

Usually, going to properties -> Open with and then selecting the desired program does it. But what if the application (here, Adobe Acrobat) isn’t there? Here’s the little trick that solved my problem (in Gnome):

Open the file /etc/gnome/defaults.list (admin mode).

Change the line:
application/pdf=evince.desktop

to:
application/pdf=acroread.desktop

Done.