Set up a multilevel list of headings, where you assign level 7/Heading 7 (for example) for your appendixes. See the "Example 1" section of the article at http://support.microsoft.com/kb/290953/en-us/ (How to number chapters, appendixes, and pages in documents that contain both chapter and appendix headings in Word).

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Stefan Blom
Microsoft Word MVP

Microsoft 365 apps for business
Windows 11 Professional