You don't start it manually. It's set to open particular formats. I'm not sure of which one's exactly on the EZReader but fb2 at minimum.
I believe that by default, pdf and epub are opened by the adobe software, but you can open epub formatted books with coolreader by adding the .fb2 extension after the epub extension. At least that's what I've read on the forum, but haven't tried it myself.
Coolreader is an e-book viewer. More details here
Coolreader.