Where can my Add-In see into the file text?

I've been making an add-in for VS2013. It's hooked into DocumentEvents through theEnvDTE, and I've been using the namespace to map out the entire project when I need to, but I can't seem to find a way to actually start looking into the text of the files in the project. I need to look at some text that's at the top of certain files. I can find the files fine, I just need a way to look into them.

So, is there something in the EnvDTE that I'm missing? Or am I looking for another namespace?