KLK1

This plugin lets you generate a hundred posts on your blog. It was built for testing purposes, where generating lots of random posts may prove useful.

PostsGenerator

mirgcire

stianlik

This plugin hooks into the media manager and generates a thumbnail everytime a 
PDF is uploaded. Generated thumbnail is an image of the first page in the 
uploaded document and is named <code>PDFNAME-thumbnail</code>, where <code>PDFNAME</code> is replaced 
by uploaded document filename.
Generated thumbnails are equivalent to <a href="https://codex.wordpress.org/Post_Thumbnails" rel="nofollow ugc">featured 
images</a> so that common thumbnail 
functions like <code>get_post_thumbnail_id()</code> can be used for PDF attachments. See 
<a href="https://codex.wordpress.org/Post_Thumbnails" rel="nofollow ugc">Post Thumbnails</a> for information 
on how you can use thumbnails efficiently.
Integration with the javascript media API is not yet implemented, therefore, you 
may need to reload the page before you can see generated thumbnail after an 
upload.
<h4>Shortcodes</h4>
It is possible to display a thumbnail linking to an uploaded PDF using the <code>[pdf_thumbnails_link]</code> 
shortcode. The following attributes are supported:
<ul>
<li><code>id</code> – Attachment ID (required)</li>
<li><code>size</code> – <a href="https://codex.wordpress.org/Post_Thumbnails#Thumbnail_Sizes" rel="nofollow ugc">Thumbnail size</a> (optional)</li>
<li><code>title</code> – <a href="https://developer.mozilla.org/en-US/docs/Web/HTML/Global_attributes#attr-title" rel="nofollow ugc">Anchor title attribute</a> (optional)</li>
<li><code>target</code> – <a href="https://developer.mozilla.org/en-US/docs/Web/HTML/Element/a#attr-target" rel="nofollow ugc">Anchor target attribute</a> (optional)</li>
<li><code>download</code> – <a href="https://developer.mozilla.org/en-US/docs/Web/HTML/Element/a#attr-download" rel="nofollow ugc">Anchor download attribute</a> (optional)</li>
</ul>
Example 1: Display link to PDF with ID = 172 using <a href="https://codex.wordpress.org/Post_Thumbnails#Thumbnail_Sizes" rel="nofollow ugc">default thumbnail size</a>
<pre><code>[pdf_thumbnails_link id="172"]
</code></pre>
Example 2: Display link to PDF with ID = 172 using thumbnail size (default 150×150)
<pre><code>[pdf_thumbnails_link id="172" size="thumbnail"]
</code></pre>
Thanks to <a href="https://wordpress.org/support/profile/mirgcire" rel="ugc">mirgcire</a> for providing the first 
version of the <code>[pdf_thumbnails_link]</code> shortcode.
<h4>Developer API</h4>
In most cases it should be sufficient to use built-in thumbnail functions from 
the WordPress API (<code>get_post_thumbnail</code> and similar). If you need to modify the 
way thumbnails are generated, you can override image generation with 
the <code>pdf_thumbnails_generate_image_blob</code> filter.
Example 1: Increase resolution for all generated PDF thumbnails
<pre><code>// $blob is the current image blob (defaults to null, can be used for chaining)
// $filename is the PDF filename
add_action('pdf_thumbnails_generate_image_blob', function ($blob, $filename) {
 $imagick = new Imagick();
 $imagick->setResolution(200,200);
 $imagick->readImage($filename);
 $imagick->setIteratorIndex(0);
 $imagick->setImageFormat('jpg');
 return $imagick->getImageBlob();
}, 10, 2);
</code></pre>
It is possible to modify generated thumbnail links using the <code>pdf_thumbnails_link_shortcode</code> 
filter. The following attributes are available:
<ul>
<li><code>$html</code> – Generated HTML code to be displayed</li>
<li><code>$attachmentId</code> – Sanitized ID of the PDF attachment</li>
<li><code>$size</code> – Sanitized thumbnail size</li>
<li><code>$atts</code> – <a href="https://codex.wordpress.org/Shortcode_API#Handling_Attributes" rel="nofollow ugc">Shortcode attributes (not sanitized)</a></li>
<li><code>$content</code> – Shortcode content (not sanitized)</li>
</ul>
Example 2: Wrap thumbnail link in figure and append caption
<pre><code>add_filter('pdf_thumbnails_link_shortcode', function ($html, $attachmentId, $size, $atts, $content) {
 return "<figure>$html <caption>Click to open image $attachmentId</caption></figure>";
}, 10, 5);
</code></pre>
<h3>TODO</h3>
Add generated image to media browser after upload.
Outline of an implementation based on the javascript media API:
<pre><code>// New uploads
wp.Uploader.queue.on('add', function (attachment) {

 if (attachment.subtype !== 'pdf') {
 return;
 }

 findThumbnailFor(attachment.ID).then(function (data) {

 // Add attachment thumbnail to browser
 var attachment = wp.media.model.Attachment.get(id)
 attachment.fetch().done(function () {
 wp.media.editor.open().state().get('library').add(generated attachment)
 });

 });
});
</code></pre>
Filter: ajax_query_attachments_args

PDF Thumbnails

The plugin does just what it says and the author is very helpful.  My only suggestion would be to add a short code that would insert a clickable thumbnail into a webpage.  Clicking on that would open the PDF in a viewer.
For example: [pdf-thumbnail id="1234" size="medium"]
... naturally this functionality would require host support for imagick.



Nice Job

Works just like it should. Can't believe this functionality isn't in the WP core. Thanks!

Excellent

This plugin generates a thumbnail everytime you upload a PDF attachment. Generated thumbnail is an image of the first page in uploaded document.

PostsGenerator vs PDF Thumbnails