For Microsoft Word “.docx” documents with Zotero or Mendeley citation fields that were inserted with the Word plugins from these reference managers, you can use Reference Extractor.
If you still have the references in a reference manager, you can export them from this program to a file format for exchanging bibliographic metadata, such as RIS or BibTeX, and then import this file into Zotero.
You can follow these steps to format the bibliography as BibTeX, which Zotero can import:
C:\Program Files (x86)\Microsoft Office\<Office version>\Bibliography\Style
If the references have ISBNs, DOIs, or PubMed IDs, you can also use the Add Item by Identifier function in Zotero to quickly add these items to your Zotero library.
You can parse plain-text bibliography references using AnyStyle, an online bibliography parser that can be trained for improved results. Export parsed citations as BibTeX or CiteProc/JSON and import into Zotero. Additional plain-text reference parsers are listed below.
Otherwise, your best option is to find the items online in a repository that Zotero supports, or, as a last resort, manually enter the references.
Alternative plain-text reference parsers: