The main reason I think that knowledge management must be based on a mental definition of knowledge is that, even if you identified any explicit resource that you can unambiguously call "knowledge", you are still left to explain the mental phenomenon of understanding, which is essentially a different thing. If you are to call both the resource and the understanding "knowledge", then you would start with a confusing definition of the fundamentals. In particular, because understanding can be achieved not only by analyzing documents, but also by many other techniques based on reflection and socialization, such as lectures, mentoring, webinars, etc. Should we call all of them "knowledge" as well? I don't think so.

Different types of knowledge have been suggested within the mental domain, and it's a complex discussion I leave for another moment, however, just like there are different sensory qualia (olfactory, visual, etc.) the question of which are the types of knowledge qualia remains open.

Defining "knowledge" only as a mental event becomes necessary because eliciting understanding is precisely what KM is about, that is, to facilitate through the most effective ways that the employee learn the skills aligned with corporate goals. 

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https://pixabay.com/en/thought-idea-innovation-imagination-2123970/