Are you sure they're manual line breaks and not paragraph breaks? If you click on the ¶ symbol on the Ribbon's Home tab, manual line breaks will look like ↵ and paragraph breaks will look like ¶.
For a general-purpose clean-up macro for text pasted from web sites, emails, PDFs, etc, see:
https://www.msofficeforums.com/word/...html#post32907