Adams and Aizawa often write that what distinguishes cognitive processes from non-cognitive processes is that the former involve representations with non-derived content.
But as Clark points out somewhere (help wanted on this ref), this is probably too loose. When Otto uses his notebook, there are presumably mental representations in his brain that have non-derived content, so that his use of the notebook in some sense involves representations with non-derived content
Yet, an appropriate clarification of the target concept is ready to hand in terms of the idea of a vehicle of content. (For its use in the context of the extended cognition debates, see, e.g., (Hurley, 1998).) The idea is that cognitive vehicles of content must bear non-derived content, so that the vehicles of content in cognitive processes must bear non-derived content. That seems to work to rule out Otto's use of his notebook involving representations in the relevant sense.
Hurley, S. (1998). Vehicles, contents, conceptual structure, and externalism. Analysis, 58(1), 1-6.