Why doesn't require work?

Question

Yii

My code snippet where I am trying to use the fpdf library to work with pdf files. The thing is, I am getting the following error Class 'app\models\FPDF' not found. If you refuse to use the namespace, everything becomes fine, but my main code is built on this. How to get around this problem?

namespace app\models;

use Yii;
use yii\base\Model;

require('.\..\vendor\setasign\fpdf\fpdf.php');
$envelope = __DIR__ .'\images\konvert-6.jpg';
$img = ImageCreateFromJPEG($envelope);
$pdf=new FPDF();
$pdf->AddPage();
$pdf->SetFont('Arial','B',16);
$pdf->Image($envelope,60,30,90,0);
$pdf->Output();

Answer 1

composer require setasign/fpdf:^1.8
in the console in the code For review
use setasign\Fpdf

Answer 2

require works for you, otherwise it would swear at it. You are calling $pdf=new FPDF(); being in app\models namespace, you should call $pdf=new \FPDF(); or specify the name of the FPDF class with namespaces if it has them