How do I add files to third party apps?

Hey guys,

I recently updated iTunes to 12.1. I needed to add some pdf files to my iPad for a class. In previous versions of iTunes, I would just click the app tab and there would be a section for Adobe Reader/Acrobat where I could click and drag the file. Now that I've updated, I can't seem to find that section. How do I add files? Thanks in advance.