Download file from GridView

 this is my grid view
<asp:GridView ID="GVReceivedDocuments" runat="server"
                              DataKeyNames="EntreeInDocID"
                      AutoGenerateColumns="False"
    AlternatingRowStyle-BackColor="#A0A0A0" AllowPaging="True">
    <PagerStyle CssClass="cssPager" />
                      <Columns>
                  <asp:BoundField HeaderText="From" DataField=& ...