We’re in the process of updating the documentation for Zotero 5.0. Some documentation may be outdated in the meantime. Thanks for your understanding.
Why do I see code beginning with ADDIN ZOTERO_ITEM CSL_CITATION in my Word document instead of formatted citations?
Word is displaying field codes instead of formatted fields. To toggle this mode, press Alt-F9 (Windows) or Option-F9/Option-Fn-F9 (Mac). You can also Select All, right-click, and choose Toggle Field Codes in the context menu, or change the setting from the Word preferences.