When your cursor is at the end of a paragraph, and you press the Enter key, the style of the next paragraph depends on an attribute in the style called "Style for following paragraph". That part is easy to change by modifying the setting on the Heading 4 style.

Now, setting up the numbering on the style for the paragraphs that follow is the hard part. There are numerous links on this forum to the Shauna Kelly numbered list instructions. I would recommend you include the following style as part of the outline list used for the headings but you will need to examine whether you ever need a Heading 5 in your document (and whether you need numbered lists under other heading levels).

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Andrew Lockton
Chrysalis Design, Melbourne Australia