ParagraphFormat.LineSpacingRule (Word)

Returns or sets the line spacing for the specified paragraph formatting. Possible return values are wdLineSpace1pt5 - Space-and-a-half line spacing. Spacing is equivalent to the current font size plus 6 points, wdLineSpaceAtLeast - Line spacing is always at least a specified amount. The amount is specified separately, wdLineSpaceDouble - Double spaced, wdLineSpaceExactly - Line spacing is only the exact maximum amount of space required. This setting commonly uses less space than single spacing, wdLineSpaceMultiple - Line spacing determined by the number of lines indicated, wdLineSpaceSingle - Single spaced. default.

Use wdLineSpaceSingle, wdLineSpace1pt5, or wdLineSpaceDouble to set the line spacing to one of these values. To set the line spacing to an exact number of points or to a multiple number of lines, you must also set the LineSpacing property.

ActiveDocument.Paragraphs(1).LineSpacingRule = _ 
 wdLineSpaceDouble