Metadata is data that describes an item. For example, author, title, journal title, date, and the DOI or URL, are common pieces of metadata needed to create a citation.
The quality of the resulting citation depends on the accuracy and completeness of the metadata provided by the source. Zotero does not create or correct the metadata. You are responsible for verifying the metadata. Garbage in, garbage out.
You can't create a citation from a stand-alone PDF with no metadata. The item needs to have the Info Tab with metadata in it for citing.
Make necessary edits in Zotero, not in Word
Preview the citation in Zotero for accuracy, and fix formatting before citing in Word.
You're only going to be using one citation style, so removing styles you aren't using will save you time.
Remove a style:
Add a style: