word-table-fill-empty-cells

Sub ProcCells1()
    Dim tTable As Table
    Dim cCell As Cell
    Dim sTemp As String

    sTemp = "-"

    For Each tTable In ActiveDocument.Range.Tables
        For Each cCell In tTable.Range.Cells
            'An apparently empty cell contains an end of cell marker
            If Len(cCell.Range.Text) < 3 Then
                cCell.Range = sTemp
            End If
        Next
    Next
    Set oCell = Nothing
    Set tTable = Nothing
End Sub