It depends on why I need to read it. If I'm adding a third-party library with specific functionality to my code and it's not working quite right, I typically grep for terms I'm nearly positive will appear somewhere in the code specific to the functionality I'm interested in. Then I look at each one of those until I find what I want. If that doesn't work, I try to find the starting point in the code and follow it until I find what I need. This works for me most of the time.