CakePHP RequestHandler: setContent/renderAs/respondAs .. what?

Can someone please explain these functions:

 RequestHandlerComponent::renderAs()
 RequestHandlerComponent::respondAs()
 RequestHandlerComponent::setContent()

It feels slightly redundant to have all three of them (as public methods anyway). If I want to respond to a request with a PDF file, does that mean I'd have to call all three functions? How should I use these in my controller?