The built-in Headings all have an unchangeable Outline Level which is the setting that determines the bookmarks in Acrobat (when using Save As PDF with options set to make headings bookmarks).

To avoid the lower level headings going in to the Acrobat bookmarks you have two choices:
1. Use alternative styles for those headings which you can set to have an outline level = Body Text
2. Put those headings into Table cells (with no fill or borders). For some reason headings in tables won't become bookmarks in Acrobat.

Note that both these options will hide those headings if you are in the habit of using the Navigation Pane to view the headings so it has an impact in how you use the Word document too.

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Andrew Lockton
Chrysalis Design, Melbourne Australia