Hide a column in the VB Code behind

                                    <telerik:RadGrid ID="RadGridMaterials" runat="server" AllowPaging="True" AllowSorting="True" GridLines="None" Width="896px" PageSize="20">
                                        <PagerStyle Mode="NextPrevNumericAndAdvanced" />
                                        <MasterTableView AutoGenerateColumns="false" TableLayout="Fixed">
                                            <NoRecordsTemplate>
                                                No Material Records Found
                                            </NoRecordsTemplate>
                                            <Columns>
                                                <telerik:GridButtonColumn ButtonType="PushButton" HeaderText="" HeaderStyle-Width="50px" UniqueName="EditItem" Text="Edit" ConfirmText="Edit Item?" CommandName="EditItem" />
                                                <telerik:GridBoundColumn  DataField="itemsku" HeaderText="ID" HeaderStyle-Width="120px" />
                                                <telerik:GridBoundColumn  DataField="itemdesc" HeaderText="Description" HeaderStyle-Width="380px" />
                                                <telerik:GridBoundColumn  DataField="itemquantity" HeaderText="Quantity" HeaderStyle-Width="50px" ItemStyle-HorizontalAlign="Right" />
                                                <telerik:GridButtonColumn ButtonType="ImageButton" HeaderText="Adjust Quantity" HeaderStyle-Width="70px" HeaderStyle-HorizontalAlign="Center" ItemStyle-HorizontalAlign="Center" UniqueName="EditQty" ImageUrl="~\images\Edit-32.png" CommandName="EditQty" />
                                                <telerik:GridButtonColumn ButtonType="ImageButton" HeaderText="Rename" HeaderStyle-Width="70px" HeaderStyle-HorizontalAlign="Center" ItemStyle-HorizontalAlign="Center" UniqueName="Rename" ImageUrl="~\images\Edit-32.png" CommandName="Rename" />
                                                
                                                <%--<telerik:GridButtonColumn ButtonType="ImageButton" HeaderText="Preview" HeaderStyle-Width="60px" HeaderStyle-HorizontalAlign="Center" ItemStyle-HorizontalAlign="Center" UniqueName="Preview" ImageUrl="~\images\transparent.png" />--%>
                                                <telerik:GridTemplateColumn HeaderText="Preview" HeaderStyle-Width="50px">
                                                    <ItemTemplate>
                                                        <button id="Preview" type="button" data-toggle="modal" data-target="#renderingPDF" class="previewbutton">
                                                            <img src="/images/Adobe-32.png"
                                                        </button> 
                                                    </ItemTemplate>                                                
                                                </telerik:GridTemplateColumn>
                                                
                                                <telerik:GridButtonColumn ButtonType="ImageButton" HeaderText="Download" HeaderStyle-Width="60px" HeaderStyle-HorizontalAlign="Center" ItemStyle-HorizontalAlign="Center" UniqueName="Download" ImageUrl="~\images\transparent.png" />
                                                <telerik:GridButtonColumn ButtonType="ImageButton" HeaderText="Delete" HeaderStyle-Width="48px" HeaderStyle-HorizontalAlign="Center" ItemStyle-HorizontalAlign="Center" UniqueName="DeleteItem" ImageUrl="~\images\Garbage-Closed-32.png" ConfirmText="Delete Item?" CommandName="DeleteItem" />
                                                <telerik:GridBoundColumn  DataField="PDF" Display="false" UniqueName="PDF" />
                                                <telerik:GridBoundColumn  DataField="CartContentPk" Display="false" UniqueName="CartContentPk" />
                                                <telerik:GridBoundColumn  DataField="SavePk" Display="false" UniqueName="SavePk" />
                                                <telerik:GridBoundColumn  DataField="Type" Display="false" UniqueName="Type" />
                                                <telerik:GridBoundColumn  DataField="EventOrderItemsId" Display="false" UniqueName="EventOrderItemsId" />
                                                <telerik:GridBoundColumn  DataField="EventLinkPK" Display="false" UniqueName="EventLinkPK" />
                                            </Columns>
                                        </MasterTableView>
                                    </telerik:RadGrid>

  Private Sub RadGridMaterials_ItemDataBound(ByVal sender As Object, ByVal e As Telerik.Web.UI.GridItemEventArgs) Handles RadGridMaterials.ItemDataBound
            Try
                If TypeOf e.Item Is GridDataItem Then

                    Dim dataItem As GridDataItem = TryCast(e.Item, GridDataItem)
 '----------------------------------------------------------------------------------------------

                    'Dim btnPreview As button = TryCast(dataItem("Preview").Controls(0), button)
                    Dim btnPreview As HtmlButton = New HtmlButton
                    ' Try
                    btnPreview = CType(dataItem.FindControl("Preview"), HtmlButton)
                    'Catch ex1 As Exception
                    'LogException(New Exception("Define Button Preview" & ex1.Message.ToString))
                    'End Try

                    Try
                        If dataItem("PDF").Text = " " Or dataItem("CartContentPk").Text = " " Then
                            'btnPreview.Enabled = False
                            'btnPreview.ImageUrl = "~\images\transparent.png"
                            btnPreview.Visible = False
                        Else
                            'btnPreview.ImageUrl = "~\images\Adobe-32.png" 'Stuffed_Folder.png"
                            'btnPreview.Enabled = True
                            'btnPreview.ToolTip = dataItem("ItemSKU").Text
                            btnPreview.Visible = True
                            'btnPreview.OnClientClick = "window.open('" & dataItem("PDF").Text & "','','')"
                        End If
                    Catch ex As Exception
                        LogException(ex)
                    End Try

                    '----------------------------------------------------------------------------------------------
                End If

            Catch ex As Exception
                lblErrMessage.Text = ex.ToString
            End Try
        End Sub