Sub Demo()
Application.ScreenUpdating = False
Dim Tbl As Table, r As Long
For Each Tbl In ActiveDocument.Tables
  With Tbl
    For r = 1 To .Rows.Count
      If .Rows(r).Cells.Count = 3 Then
        With .Cell(r, 3).Range
        'Do whatever with the 3rd cell
        End With
      End If
    Next
  End With
Next
Application.ScreenUpdating = True
End Sub