I trust you're not using what Microsoft calls Master documents. These are a long standing source of catastrophic document corruption. See:
Why Master Documents corrupt
Master Documents Feature in Microsoft Word - from the Frequently Asked Questions (FAQ) about Microsoft Word
If you want to link contents from multiple documents together, that can be done via Word's INCLUDETEXT field - which is what Word creates for you if you use Insert|Object|>Text from File>Insert as Link. See: Field codes: IncludeText field - Office Support

Word also provides an RD field which allows you to have a Table of Contents in one document that references content in another document. See: Field codes: RD (Referenced Document) field - Office Support

You may also find https://www.msofficeforums.com/word/...nal-files.html helpful when using INCLUDETEXT & RD fields to link documents that may need to be moved around.

__________________
Cheers,
Paul Edstein
[Fmr MS MVP - Word]