Change requests are project documents, typically consolidated into a change log and electronically stored in most modern change control systems. I can't speak to why the PMBOK Guide doesn't separate it out; it doesn't matter for the exam, simply know that the CCS is used to monitor and control the changes to the project baselines.
The Plan Risk Response process has the following output:
Project Documents Updates
which lists as one of its components "Change Requests"! (PMBOK v.5, page 348)
My question:
(1) Are Change Requests Project Documents?
(2) Why not simply make them a separate output of this process, as is done for other processes? Why include change requests in project documents?
Training for Project Management Professional (PMP)®, PMI Agile Certified Practitioner (PMI-ACP)®, and Certified Associate in Project Management (CAPM)®