Lots of strange symbols in the code above, try with the below - no strange symbols in the code.

Sub Sample()    Dim MyArray() As String
    Dim n As Long, i As Long
    Dim Col As New Collection
    Dim itm


    n = 0
    ' Get all the sentences from the word document in an array
    For i = 1 To ActiveDocument.Sentences.Count
        n = n + 1
        ReDim Preserve MyArray(n)
        MyArray(n) = Trim(ActiveDocument.Sentences(i).Text)
    Next


    ' Sort the array
    SortArray MyArray, 0, UBound(MyArray)


    ' Extract Duplicates
    For i = 1 To UBound(MyArray)
        If i = UBound(MyArray) Then Exit For
        If InStr(1, MyArray(i + 1), MyArray(i), vbTextCompare) Then
            On Error Resume Next
            Col.Add MyArray(i), """" & MyArray(i) & """"
            On Error GoTo 0
        End If
    Next i


    ' Highlight duplicates
    For Each itm In Col
        Selection.Find.ClearFormatting
        Selection.HomeKey wdStory, wdMove
        Selection.Find.Execute itm
        Do Until Selection.Find.Found = False
            Selection.Range.HighlightColorIndex = wdPink
            Selection.Find.Execute
        Loop
    Next
End Sub


' Sort the array
Public Sub SortArray(vArray As Variant, i As Long, j As Long)
  Dim tmp As Variant, tmpSwap As Variant
  Dim ii As Long, jj As Long


  ii = i: jj = j: tmp = vArray((i + j) \ 2)


  While (ii <= jj)
     While (vArray(ii) < tmp And ii < j)
        ii = ii + 1
     Wend
     While (tmp < vArray(jj) And jj > i)
        jj = jj - 1
     Wend
     If (ii <= jj) Then
        tmpSwap = vArray(ii)
        vArray(ii) = vArray(jj): vArray(jj) = tmpSwap
        ii = ii + 1: jj = jj - 1
     End If
  Wend
  If (i < jj) Then SortArray vArray, i, jj
  If (ii < j) Then SortArray vArray, ii, j
End Sub