Are you using Acrobat to create your material? Really it isn't for that. Use the same app you would have used to make paper adverts (eg. Word, InDesign, Publisher) and convert to PDF. Editing PDF is a desperate last resort, despite Adobe's marketing.
Sorry, I think my reply was nonsense. I thought I was in the Acrobat forum. Since it's InDesign - which is PERFECT for this! - my question is - why would you press RETURN at the end of a line? But if you must make a short line, how about a soft return, Shift+RETURN. And if I've got that completely wrong too, I'll just go and hide.