Are you saying that you pressed Return/Enter once for a new "line" of text and twice for each new paragraph? In that case, first Replace All ^p^p with, say, ///. Then Replace All ^p with a space. Finally, replace all /// with ^p.

In the Find and Replace dialog box (Ctrl+H), ^p represents a paragraph mark (¶ with nonprinting marks displayed).

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Stefan Blom
Microsoft Word MVP

Microsoft 365 apps for business
Windows 11 Professional