The following should work
Sub Highlight_WordN()
Dim oRng As Range
    Set oRng = ActiveDocument.Range
    With oRng.Find
        Do While .Execute(FindText:="Contractor Shall")
            oRng.Sentences(1).HighlightColorIndex = wdYellow
            oRng.Collapse 0
        Loop
    End With
lbl_Exit:
    Set oRng = Nothing
    Exit Sub
End Sub