eclev91

This will quickly tell your server has all the software installed to take advantage of WordPress 4.7’s built-in PDF thumbnail generation. Some plugins may shim the functionality in other ways. This test only concerns the native WordPress functionality.
From <a href="https://sternerstuffdesign.com" rel="nofollow ugc">Sterner Stuff Design</a>.
Tests: 
* ImageMagick 
* Imagick PECL Extension 
* GhostScript 
* Your WordPress Version

PDF Thumbnails Support Test

Determine if your server is missing software for WordPress 4.7's native PDF thumbnail generator.

Dave Ligthart

A simple way to choose a default thumbnail for your post.
Works alongside the featured image core functionality.
For theme usage:
<h4>Add this function where you want the thumbnail to appear</h4>
<pre><code><?php if(function_exists('wct_thumb')){ wct_thumb(); } ?>
</code></pre>

WP-Choose-Thumb

A simple way to add a default thumbnail to your post.

PDF Thumbnails Support Test vs WP-Choose-Thumb