Why doesn't imagick work when converting to pdf?

Question

PHP

Imagick 3.4.4
ImageMagick 6.8.9-9 Q16 x86_64 2019-06-15
When converting png to pdf, it gives empty space. The method returns true in this case
. There are no problems with other formats.
Maybe someone came across?

$imageick = new \Imagick();

        ob_start();
        imagepng($this->im);
        $image_data = ob_get_contents();
        ob_end_clean();

        $imageick->readimageblob($image_data);
        $imageick->setFormat('pdf');
        $response = new Response($imageick->getImageBlob());
        $response->headers->set('Content-Type', 'application/pdf');
        $response->headers->set('Content-Disposition', 'inline; filename="'.$code.'"');
        return $response;

Answer 1

Some formats have dangerous vulnerabilities.
Debian, for example, solved PDF problems by disabling ImageMagick from working with PDFs. Not your case?
Settings in /etc/ImageMagick-6/policy.xml, line with PDF - rights "none" should be changed to rights "read|write"