asp:GridView ID="GridViewAttachment" runat="server" AutoGenerateColumns="False" SkinID="ListGridViewStyle" DataSourceID="ObjectDataSource1"  onRowDataBound=gv_RowBound>   

protected void gv_RowBound(object sender, GridViewRowEventArgs e)
    {
 
                //System.Web.UI.WebControls.Image img = (System.Web.UI.WebControls.Image)e.Row.Cells[0].FindControl("imgPDF");// Controls[0];
               
               //this one for button field type image
               System.Web.UI.WebControls.Image img = (System.Web.UI.WebControls.Image)e.Row.Cells[0].Controls[0];//.FindControl("imgPDF");// Controls[0];
   
              //this one for button field type link
              //System.Web.UI.WebControls.LinkButton btn = (System.Web.UI.WebControls.LinkButton)e.Row.Cells[8].Controls[0];//.FindControl("imgPDF");//Controls[0];

                object dataItem = e.Row.DataItem;
                 string Path = DataBinder.Eval(dataItem, "Attachment_Path").ToString();
 

                if (Path == "")
                {
                   
                    img.ImageUrl = "Images/noPic.gif";
                    img.Attributes.Add("OnClick", "alert('There is no attached document');return false;");
                }
                else
                {

                    Path = Path.Trim().Replace("\\", "\\\\");

                    img.Attributes.Add("OnClick", "return openPDF('" +_docPath + Path + "');return false;"); //openPDF is a javascript function
                   
                }
                e.Row.Cells[0].ToolTip = "Click on the PDF icon to open up the document";
          
            }
            catch (Exception ex) { }
        }
    }

//Javascript function
function openPDF(path)
{
    var opt_windowFeatures = "location=1,status=1,scrollbars=1, resizable=1, width=600, left=670";
    try
    {
      window.open (path, '', opt_windowFeatures);
    }
    catch (err){}
    return false;
}

HI,

Thanks for giving reply. I need to open the file on hyperlink click. The above code I did,'t understand. Please post in vb.net so that its useful for me. Plz help me regarding this

Thanks

</body>
<script>
function openPDF(path)
{
    var opt_windowFeatures = "location=1,status=1,scrollbars=1, resizable=1, width=600, left=670";
    try
    {
      window.open (path, '', opt_windowFeatures);
    }
    catch (err){}
    return false;
}
</script>
</html>

-----------------
asp:GridView ID="GridViewAttachment" runat="server" AutoGenerateColumns="False" SkinID="ListGridViewStyle" DataSourceID="ObjectDataSource1"  onRowDataBound=gv_RowBound>
-----------------

  Protected Sub RowDataBound(ByVal sender As Object, ByVal e As GridViewRowEventArgs)
        Dim link As System.Web.UI.WebControls.HyperLink
        Dim _docPath As String = "path to image"
        For Each ctrl As System.Web.UI.Control In e.Row.Cells(0).Controls
            link = ctrl.FindControl("Hyperlink1")
            If (link.Text <> "") Then

                Dim dataItem As Object = e.Row.DataItem
                Dim Path As String = DataBinder.Eval(dataItem, "Attachment_Path").ToString()

                If (Path = "") Then

                    link.ImageUrl = "Images/noPic.gif"
                    link.Attributes.Add("OnClick", "alert('There is no attached document');return false;") '
                Else

                    Path = Path.Trim().Replace("\\", "\\\\")

                    link.Attributes.Add("OnClick", "return openPDF('" + _docPath + Path + "');return false;") ' //openPDF is a javascript function

                End If
                e.Row.Cells(0).ToolTip = "Click on the PDF icon to open up the document"

            End If
        Next ctrl

    End Sub

Try that and see