How activated fonts are found by other apps?

Question

Fist of all, my os is mac. 
I ask this question because I am surprised that fonts activated in adobe creative clouds are usable with other apps such as the Word without be listed in the font book app. To be more specific, the activated fonts are downloaded in a hidden folder whose path is XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX, and the file names are just fonts id.
How is this possible that other apps even know the existence of the activated fonts? I can only imagine that  there might be an environmental variable containing the path of the hidden folder, but what is the environmental variable?
 
(Admin edited posting to remove proprietary information!)

Dov Isaacs · Accepted Answer

MacOS, Windows, iOS, and iPadOS (not sure about Android) all have mechanisms for “private” font installation. Both Adobe and Microsoft as well as some font foundries having similar services to Adobe Fonts use these mechanisms for installation/activation as well as removal/deactivation of fonts. As long as an application uses standard system calls to “enumerate” fonts, the application sees these private, hidden fonts.

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