Hello,
Yes, there’s probably the following reason to that..
=> You may have WordPress 4.7+ with an hosting where Imagemagick or Imagick AND ghostscript are installed. Else you will not have the new wordpress option that automatically create an image preview of your PDF stored as an attachement image. More info here:
https://make.wordpress.org/core/2016/11/15/enhanced-pdf-support-4-7/
If you don’t have this option automatically activated, there’s 2 possibilities to try:
1) you might maybe find a plugin that add the option to set a featured image to your PDF attachment… then you’ll need to manually attach the image to your PDF each time you download one.
2) Else, try the following plugin – as WP 4.7 feature – it also require Imagemagick and Ghostscript, but for an unknown reason it was working for me on a website where the default WP 4.7+ behaviour were not working:
https://fr.wordpress.org/plugins/pdf-image-generator/
I don’t have more time to investigate, but if someone has the reason why this plugin works where WP 4.7 doesn’t, i’m curious of the answer.
