I see two different requirements
Download link tracking - this will fire whenever you download a file, it could be anything, exe, pdf, Xls, etc. this you can find in your custom editor.
s.trackDownloadLinks= true;
s.linkDownloadFileTypes= 'exe,zip,wav,mp3,mov,mpg,avi,wmv,doc,pdf,xls';
With this you can track path of the link, in your case it is pdf path.
The other use case is what if you want to track pdf path along with the downloaded user name, location, etc. in this case normally we go with a custom link approach.
You need to create data elements for your fields and map it to the custom event in the Launch property.