Hi Indradeo,

Set the GridView DataKeyNames property.

On Download button click get the value from DataKeys using the selected row index.

Please refer below sample.

HTML

<asp:GridView ID="GridView1" runat="server" AutoGenerateColumns="false" DataKeyNames="Value">
    <Columns>
        <asp:BoundField DataField="Text" HeaderText="File Name" />
        <asp:TemplateField>
            <ItemTemplate>
                <asp:LinkButton ID="lnkDownload" Text="Download" runat="server" OnClick="DownloadFile"></asp:LinkButton>
            </ItemTemplate>
        </asp:TemplateField>
    </Columns>
</asp:GridView>

Namespaces

C#

using System.IO;

VB.Net

Imports System.IO

Code

C#

protected void Page_Load(object sender, EventArgs e)
{
    if (!this.IsPostBack)
    {
        string[] filePaths = Directory.GetFiles(Server.MapPath("~/Uploads/"));
        List<ListItem> files = new List<ListItem>();
        foreach (string filePath in filePaths)
        {
            files.Add(new ListItem(Path.GetFileName(filePath), filePath));
        }
        GridView1.DataSource = files;
        GridView1.DataBind();
    }
}

protected void DownloadFile(object sender, EventArgs e)
{
    int index = ((sender as LinkButton).NamingContainer as GridViewRow).RowIndex;
    string filePath = GridView1.DataKeys[index].Values[0].ToString();
    Response.ContentType = ContentType;
    Response.AppendHeader("Content-Disposition", "attachment; filename=" + Path.GetFileName(filePath));
    Response.WriteFile(filePath);
    Response.End();
}

VB.Net

Protected Sub Page_Load(ByVal sender As Object, ByVal e As EventArgs) Handles Me.Load
    If Not Me.IsPostBack Then
        Dim filePaths As String() = Directory.GetFiles(Server.MapPath("~/Uploads/"))
        Dim files As List(Of ListItem) = New List(Of ListItem)()

        For Each filePath As String In filePaths
            files.Add(New ListItem(Path.GetFileName(filePath), filePath))
        Next

        GridView1.DataSource = files
        GridView1.DataBind()
    End If
End Sub

Protected Sub DownloadFile(ByVal sender As Object, ByVal e As EventArgs)
    Dim index As Integer = TryCast((TryCast(sender, LinkButton)).NamingContainer, GridViewRow).RowIndex
    Dim filePath As String = GridView1.DataKeys(index).Values(0).ToString()
    Response.ContentType = ContentType
    Response.AppendHeader("Content-Disposition", "attachment; filename=" & Path.GetFileName(filePath))
    Response.WriteFile(filePath)
    Response.End()
End Sub

Screenshot