The manual section pertaining to Dictionary and project files could indeed use a bit a of an addendum on how to load and use project files in dictionaries and the likes.
When you use project files, your first reflex should be to add the AJAX object immediately. That's the only vanilla way of using said files to load stuff.
Documentation on AJAX object : construct.net/make-games/manuals/construct-3/plugin-reference/ajax
Basically, you use the "request project file" action, and when the request is completed, you can load the expression AJAX.LastData inside your dictionary.