When you paste in content, the formatting will adjust to the target document, assuming that both documents have the same style names. You may have to select the text and press Ctrl+SpaceBar (clears character formatting not in style) as well as Ctrl+Q (clears paragraph formatting not in style).

How did you "remove" the styles in the Styles box? I'm assuming that you are referring to the Styles "gallery" on the Home tab? If you want to reformat with a built-in set of styles, try selecting one at Home tab | Change Styles | Style Set.

When experimenting, do so on a copy of the document.

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Stefan Blom
Microsoft Word MVP

Microsoft 365 apps for business
Windows 11 Professional