One way, with no cut & paste, would be to bookmark the Common Law, Civil Law & Roman Law portions in each document - using the same bookmark names in each - then using INCLUDETEXT fields in another document to reference those bookmarks and pull in all the Common Law content in the source documents, for example. See:
https://support.office.com/en-us/art...a-2ff950fb629e


Once you've created the INCLUDETEXT field for the first source document's Common Law content, all you then need to do is replicate the INCLUDETEXT field however many times you need, change the source file's name for each copy, then press Ctrl-A, F9 to update the lot.

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Cheers,
Paul Edstein
[Fmr MS MVP - Word]