Standard way to hook into the Facebook app is a "Share Intent" which can be picked up by any other social network application; such as Google+, my text messaging app, Google Hangouts, and so many others. Even allowing "copy to clipboard" and "Pin" and whatever else. Almost every Android app creates a Share Intent listener to pull in data.

If there's a document viewer, it'll listen in for the file types it supports when you try to open a file (I think its a VIEW intent). It's all very impressive and very, very useful.