A family of Microsoft word processing software products for creating web, email, and print documents.
Ctrl K, then bottom right - "Remove"
Thanks for the follow-up. Ctrl+K displays the Hyperlink dialog box. Since removing the hyperlink fixed the problem, it seems that a large part of your document text (maybe all of it) was inside a hyperlink. Pressing Enter with the insertion point inside a hyperlink "follows" the link, that is, opens the link target, so the symptoms you described makes sense.