There is no 'horizontal line' object in Word. In Word, horizontal lines can be created as underlines, hyphens and the like, table cell borders, inlineshapes or shapes. Each kind would have to be tested for separately. Then you'd have to decide what kind of horizontal line you want to insert and how to place & size it as required.

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Cheers,
Paul Edstein
[Fmr MS MVP - Word]