Step 1: php.ini Modification
Modify or create a php.ini
file within the /public_html/
directory of the your account, adding the following line to this file…
extension=imagick.so
Step 2: .htaccess Modification
Add the following line of code to the .htaccess
file in /public_html/
SetEnv PHPRC /home/****/public_html/php.ini
Note: Be sure to replace **** with your cPanel/FTP username
Fuente: https://typewheel.xyz/wordpress-pdf-thumbnails-siteground/