If direct font formatting has been applied to more than 50% of a paragraph, it will be cleared when you (re-)apply a paragraph style, otherwise it will be retained.

And note that when you update a paragraph style to match the selection, only the font formatting included in the selection will be incorporated into the style.

To make sure that you reset all font formatting to that of the underlying style, use Ctrl+SpaceBar on the selection. Similarly, use Ctrl+Q to clear the paragraph formatting.

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Stefan Blom
Microsoft Word MVP

Microsoft 365 apps for business
Windows 11 Professional