Problems using kartik-mpdf in yii2

I'm using Kartik's mpdf in yii2, but it does not work well for me, since showing the pdf for the first time shows me rare characters like these

% PDF-1.4% 3 0 obj < > / Contents 4 0 R > > endobj 4 0 obj < > stream x [ r 3 U $ U4 - * "ѹ r D K + Z d y \ ~ 70 р R E o A I 'c G_ _ & Ǒ d ϧ n " e ѿ Fv cGo ge ׋ # - 3 # 3 wͤ \ 9 n ɍ { > ci- Z% k g. ZK gi Q 섙 f ^ ӖOv

If I update the page then I get the PDF right

What will be the problem? How do I get it right from the first time?

This is the code I use:

public function actionImprimepdf() {         
    $periodo = Periodoactivo::find()->one();
    $empresa = Empresa::find()->one();
    $modelo = VFacturacion::find()->where('Mes = :mes and Anno = :anno',[':mes' => $periodo->Mes, ':anno' => $periodo->Anno])->all();

    $content = $this->renderPartial('imprimepdf', ['modelo' => $modelo, 'empresa' => $empresa,]);

    $pdf = new Pdf([
        'mode' => Pdf::MODE_UTF8,
        'destination' => Pdf::DEST_DOWNLOAD,
        'filename' => 'pdf/Facturas.pdf',
        'content' => $content,
        'cssFile' => 'css/printfactura.css',
        'options' => ['title' => 'Facturas'],
        'methods' => [
           // 'SetHeader'=>['Krajee Report Header'],
           // 'SetFooter'=>['{PAGENO}'],
        ]
    ]);
    // return the pdf output as per the destination setting
    Yii::$app->response->format = \yii\web\Response::FORMAT_RAW;
    Yii::$app->response->headers->add('Content-Type', 'application/pdf');

    return $pdf->render();
}