Marketo Tracking Code

We utilize the reports in Marketo and for some reason the files that we have uploaded into the Marketo Design Studio aren't showing activity.  They're pdf's but they're housed inside of Marketo.  When I ask the system to look for the URL http://info.byetm.com/rs/etm/images/ETM_UPExchange_Brief.pdf it's not pulling it from the list, yet this is the link for this particular brief.  We want to see on the report when someone clicks on this link.  Any ideas why it woldn't track?  I know it's a pdf, but I was told that they would track if housed in Marketo design studio