How do I get it back to a single column?
Enable View - Status bar. Look in the right-hand corner of the Writer window and notice the icons for one page and two pages, click on the single page icon to restore the one-page view that you want.
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Tried it but it didn’t change anything. It already says it’s in one column there and under Format. It affects only documents I’ve changed from ODF to docx, and when I send it to a friend, she reads it in one column just fine.
Enable the status bar and try again.