'Not Authorized' error due to default ImageMagick policy.xml

Thanks for this useful module, just wanted to add an issue describing a minor problem I had getting this module set up in case others have the same problem. Perhaps a note could be added to the documentation for this module as I think this could be a common problem for installs that have never configured ImageMagick to read PDFs before.

Received a 'not authorized' error when attempting to use this module for the first time on Ubuntu with Nginx. At first thought it had to do with file permissions, but it turned out to be a default policy setting in ImageMagick (at least on my version of ubuntu) that disallows reading PDF files.

In:
/etc/ImageMagick-6/policy.xml

Change:
<policy domain="coder" rights="none" pattern="PDF" />
To:
<policy domain="coder" rights="read" pattern="PDF" />

Save, then restart php-fpm (if using fpm) or nginx/apache, f.x.

sudo service php7.2-fpm restart
sudo service nginx restart

or similar depending on your OS

Fixed the issue for me.

Example error from drupal included below:

Drupal\Core\Entity\EntityStorageException: not authorized `/var/www/intranet/web/sites/default/files/2019-09/test.pdf' @ error/constitute.c/ReadImage/412 in Drupal\Core\Entity\Sql\SqlContentEntityStorage->save() (line 847 of core/lib/Drupal/Core/Entity/Sql/SqlContentEntityStorage.php).

Drupal\media_pdf_thumbnail\Manager\MediaPdfThumbnailImagickManager->generateImage('/var/www/intranet/web/sites/default/files/2019-09/test.pdf', '/var/www/intranet/web/sites/default/files/2019-09/test.pdf.png') (Line: 79)
  Drupal\media_pdf_thumbnail\Manager\MediaPdfThumbnailImageManager->createThumbnail(Object) (Line: 39)
  media_pdf_thumbnail_media_presave(Object)
  call_user_func_array('media_pdf_thumbnail_media_presave', Array) (Line: 403)

...