Can an imported .STL file be broken down into individual parts (rigged) and animated in Blender? Can an imported .STL file be rigged and animated in Blender? I have a model of a house window that was given to me as a .STL file, and I want to animate how it opens/closes. FYI, I'm new to Blender and 3D animation. I want to make sure Blender is the right tool for the job.
Yes it should be possible, since importing means to convert it into Blender internal format. You can use all tools provided by Blender to work on you model. 

It could be that you need to split the window and the window frame into two objects. 
In Edit Mode select the part of the mesh you want so separate into to another object and press P this opens the Separate popup and choose Selection.