GridView On the Page
<asp:TemplateField HeaderText="File Attachment" sortExpression="strFileAttachment">
<ItemTemplate>
<p>
<%#Eval("strFileAttachment")%>
</p>
</ItemTemplate>
<EditItemTemplate>
<asp:FileUpload ID="FileUploadFileAttachment" runat="server" />
</EditItemTemplate>
</asp:TemplateField>
Core behind is
protected void GridView1_RowUpdating(object sender, GridViewUpdateEventArgs e)
{
FileUpload FileUpload1 = (FileUpload)GridView1.Rows[e.RowIndex].FindControl("FileUploadFileAttachment");
}
I think this may solve your problem.
Let me Know if it will work for you.