bind the file path in CommandArguments and write the download code in imagebutton command event
<asp:imagebutton id="btn" runat="server" commandarguments="<%#Bind("FilePaht")%>" oncommand="btn_Command" xmlns:asp="#unknown"></asp:imagebutton>
protected void btn_Command(object sender,CommandEventArgs e)
{
Response.WriteFile(MapPath(e.CommandArguments.ToString()));
Response.End();
}