Sub Insert_R_C_into_every_cell()
    Dim Rng As Range, aTable As Table, TblCell As Cell, cellvalue As String
    For Each aTable In ActiveDocument.Tables
        For Each TblCell In aTable.Range.Cells
            With TblCell
                cellvalue = "Cell_ID[" & .RowIndex & ", " & .ColumnIndex & "]"
                Set Rng = .Range
                With Rng
                    .End = .End - 1
                    .Collapse wdCollapseEnd
                    .Text = cellvalue
                    .Font.Hidden = True
                End With
            End With
        Next TblCell
    Next aTable
 End Sub