private SqlDataReader tieneDocumento(string dni)
{
SqlDataReader varCli;
SqlCommand consulta = new SqlCommand();
consulta.CommandType = CommandType.Text;
consulta.CommandText = "select 1 from [ABSTRACCIONX4].CLIENTES WHERE CLI_DNI =" + dni + " AND CLI_APELLIDO !='" + txtApe.Text + "'";
consulta.Connection = Program.conexion();
varCli = consulta.ExecuteReader();
return varCli;
}