Create in the same view (with iframe) a PDF in Codeigniter 3 with FPDF

I am new with Codeigniter and I need to generate a PDF with this library that I use frequently, I have doubts in the generation that I send by AJAX :

$.ajax({
    url:"<?php echo site_url('lecturas_pdf/')?>",
    type:"POST",  
    //dataType:"JSON",
    success:function(data){  
        alert(data);
        $('#lectura_pdf').src = data;
        //alert(data[0]);
        console.log(data);
        window.open(
            'data:application/pdf,'+encodeURIComponent(data),
            'Batch Print',
            'width=600,height=600,location=_newtab'
        );
    }
});

This is my controller:

<?php if ( ! defined('BASEPATH')) exit('No direct script access allowed');
/**
* 
*/
class Lecturas extends Castor_Controller{

    function __construct(){
        parent::__construct();
        $this->load->model('lectura');
    }
    public function index(){
        //$this->load->view('lecturas/lecturas');
        $this->load->model('barrio');
        $data['barrio']=$this->barrio->findAll();
        $data['view']='lecturas/lecturas';
        $data['output']='';
        $this->load->view('layouts_backend_lte_datatables/main', $data);        
    }
    public function listar_clientes(){
        $barrio_id = $this->input->post('barrio_id');
        $mes_consumo = $this->input->post('mes_consumo');
        $list = $this->lectura->medidor_barrio($barrio_id);

        foreach ($list as $medidor) {
            $consumo = $this->lectura->lectura_mes($medidor->id, $mes_consumo);
        }
    }
    public function listar_clientes_data(){
        $barrio_id = $this->input->post('barrio_id');
        $mes_consumo = $this->input->post('mes_consumo');

        $list = $this->lectura->get_mes_consumo($barrio_id, $mes_consumo);

        $no=0;
        $output =  '<div class="table-responsive">';  
        $output .= '<table class="table table-bordered">';  
        $output .= '<tr>';  
        $output .= '<th width="5%">Ord</th>'; 
        $output .= '<th width="36%">Nombre</th>';  
        $output .= '<th width="18%">Medidor</th>';  
        $output .= '<th width="18%">Lectura anterior</th>';  
        $output .= '<th width="18%">Lectura nueva</th>';  
        $output .= '<th width="50%">Est</th>';  
        $output .= '</tr>';

        foreach ($list as $data) {
            $no++;
            $output .= '<tr>';   
            $output .= '<td>'.$no.'</td>';   
            $output .= '<td>'.$data->apellido.'</td>';   
            $output .= '<td>'.$data->codigo.'</td>';   
            $output .= '<td class="data" data-id2="'.$data->id.'" contenteditable></td>';  
            $output .= '<td class="lectura_actual" data-id3="'.$data->id.'" contenteditable></td>';  
            //$output .= '<td class="lectura_anterior" data-id2="'.$data->id.'" contenteditable>'.$data->lectura_anterior.'</td>';  
            //$output .= '<td class="lectura_actual" data-id3="'.$data->id.'" contenteditable>'.$data->lectura_actual.'</td>';  
            $output .= '<td></td>';   
            $output .= '</tr>'; 
        }
        $output .= '</table></div>';  

        echo $output;
    }
}
?>

This is the exit:

%PDF-1.3
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<</Type /Page
/Parent 1 0 R
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endobj
4 0 obj
<</Filter /FlateDecode /Length 558>>
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