https://demos.krajee.com/mpdf

use kartik\mpdf\Pdf;
 
...
$html = $this->renderPartial('/kandydaci/umowa-pdf', [
    'model' => $model,
        ]);
 
$pdf = new Pdf([
    'mode' => 'utf-8',
    'marginLeft' => 15,
    'marginRight' => 15,
    'format' => Pdf::FORMAT_A4,
    'orientation' => Pdf::ORIENT_PORTRAIT,
    'destination' => Pdf::DEST_BROWSER,
    'content' => $html,
    //'cssFile' => '@vendor/kartik-v/yii2-mpdf/assets/kv-mpdf-bootstrap.min.css',
    'cssInline' => '.cent{
                            width:100%;
                            text-align:center;
                            margin-bottom:0;
                            margin-top:3px;
                        }
 
                        ol{
                            margin-top: 0;
                            margin-bottom: 0;
                        }',
    // set mPDF properties on the fly
    'options' => ['title' => $nazwa_pliku],
    'filename'=>$nazwa_pliku,
    // call mPDF methods on the fly
    'methods' => [
        // 'SetHeader' => ['Krajee Report Header'],
        'SetFooter' => ['|Strona {PAGENO} z {nbpg}|'],
    ]
        ]);
 
Yii::$app->response->format = \yii\web\Response::FORMAT_RAW;
Yii::$app->response->headers->add('Content-Type', 'application/pdf');
 
return $pdf->render();