ParagraphFormat.ReadingOrder (Word)

Returns or sets the reading order of the specified paragraphs without changing their alignment. Possible return values are wdReadingOrderLtr - Left-to-right reading order, wdReadingOrderRtl - Right-to-left reading order.

Use the LtrPara, LtrRun, RtlPara, and RtlRun methods of the Selection object to change the paragraph alignment along with the reading order.

ActiveDocument.Paragraphs(1).ReadingOrder = _ 
 wdReadingOrderRtl