How to link a pdf file to a specific feature with QGIS?

I'm trying to link a pdf to a parcel (see image: http://imgur.com/RbauB3v) where you click on one parcel and a specific pdf comes up and if you click on another then a different pdf comes up.

I've got it so far that if you click on a parcel it shows a pdf but the problem is that is shows the same pdf for every parcel!

Is there anyway I can assign it to just one parcel by lets say the objectid?

I'm having trouble setting the action so that it opens each parcel.