On button click save all the values of particular rows in session variables
and on page load of second page fill the disered textboxes with these session variables. like
protected void imgbtnedit_Click(object sender, EventArgs e)
{
GridViewRow Row=((Button)sender).Parent.Parent as GridViewRow;
int index=Row.RowIndex;
Session["Value1"]=((Label)grdpages.Rows[index].FindControl("ValueOfColumns1")).Text;
Session["Value2"]=((Label)grdpages.Rows[index].FindControl("ValueOfColumns2")).Text;
...
...
...
Response.Redirect("editpage.aspx");
}
and on page load of editpage.aspx
textbox1.text=Convert.ToString(session["value1"]);
...
...