View.MarkupMode (Word)

Returns or sets a WdRevisionsMode constant that represents the display mode for tracked changes. Possible return values are wdBalloonRevisions - Displays revisions in balloons in the left or right margin, wdInLineRevisions - Displays revisions within the text using strikethrough for deletions and underlining for insertions. This is the default setting for prior versions of Word, wdMixedRevisions - Not supported.

ActiveWindow.View.MarkupMode = wdBalloonRevisions