Download tracking on a site through tag manger

I have a client whose site I've been trying to set up download tracking for on PDFs they host on their wordpress site. I've been trying to do this with regEx looking for .pdf in the URL but it doesn't seem to be firing.

I've been trying to do this through tag manager but not having much luck. Would this be something you could help with?

Would it fit in an hours work do you think?
Cheers
Chris