What is the difference between Command Reference Guides and the Canon Printer Driver and Fax Driver SDKs?

The Command Reference Guides provide simple commands that can be embedded within a print job to control page and job features.
PCL Commands (Paper Selection, Cassette Selection, Font, Font Size, etc.), PJL Commands (Sorting, Stapling, Duplexing, Number of Copies, etc.) and Postscript Commands are supported by these guides.
These commands can be used on a number of operating systems to modify a print job that is destined for a Canon print device.

The Printer and Fax Driver SDKs are high-level programming instructions that can be used in applications running on a Windows OS. The SDKs allow the application to make settings that are otherwise available through the device driver User Interface. Using the SDKs requires programming skills and knowledge of certain software technologies, as described in the "Development Tools" sub-menus under the "Products" menu Tab.