If you include CKEditor inside an application with its own copyright, the terms must clearly identify which parts of the code are not bound by your copyright. Otherwise, nothing needs to be mentioned.
In any case, it is forbidden to alter or remove any of the original copyright notices and LICENSE.md file.
Please note the Open Source license comes with a small “Powered by CKEditor” logo in the bottom-right corner of the editing area. This approach is designed to make sure the entire community knows who is powering and modernizing their rich text editor.