WordPress PDF Preview Images requires ImageMagick to work



How to install imagemagick for php7 on Ubuntu?

Creating and displaying preview images of PDF files relies on these packages that need to be installed on your server :

  • ImageMagick
  • Imagick
  • Ghostscript

To install all of these modules run:

sudo apt-get install php-imagick

To make the change take effect, restart Apache:

sudo service php7.0-fpm reload

More details in this article:

Using the New PDF Preview Images in WordPress 4.7 in the Real World

Enhanced PDF Support in WordPress 4.7