Try this . . . .

<asp:TemplateField HeaderText="Thank You Letter">

<ItemTemplate>

<asp:Label ID="lblTYLetter" runat="server" Text='<%# DataBinder.Eval(Container.DataItem, "Description").ToString().PadRight(80).Substring(0,80).TrimEnd() %>'></asp:Label>

</ItemTemplate>

</asp:TemplateField>