Can’t happen. Office files are COMPLETELY different than files handled by Notepad++.
Notepad++ treats files as a sequence of letters/symbols with “new line” indicators in between. All coloring and highlighting are NOT part of the file they are “computed” during display and “lost” when file is saved.
Word processing files are extremely complicated. They are made of many different sections: text sections, formatting sections, embedded objects (like pictures) sections. The word processor combines all of these in order to present a Wysiwyg view.
The “engine” of Notepad++ and Word are completely different. Each has its pros and cons but Notepad++ just cannot be extended for this purpose.