There are no more thumbnails for uploaded PDFs

[10rjulienk21]

My current WP configuration

• PHP / MySQL version: 7.4
• Theme used: Camp Maine of TAM’S TRADING POST (no longer maintained)
• Extensions in place: activated: Akismet - BackWPup - contact Form 7 - Cookie Notice - Honeypot for Contact Form 7 - Ithemes Security - Post Type Switcher - SF Move Login - TablePress - WP Image Zoom - WP Maintenance Mode.

Name of the host: OVH
Site address: ​https://amapdlacrau.fr
Problems encountered:
The latest .PDF files uploaded to the media library have a generic file icon and no longer display the small thumbnail unlike older files. Clicking on the icon no longer opens the image of the 1st page of the file.
Everything I did that didn't work to fix the problem:

• Create PDFs with different tools; Microsoft, Do PDF, ApowerPDF ...
• Install WordPress version 5.8.1
• Downgrading the PHP version from PHP 8 to PHP 7.4 This fixed the problem with the imagik module, declared absent by the site health check in version 8, but not the thumbnail problem.
• Use an upload plugin: File Manager
• Use thumbnail regeneration plugins: Regenerate Thumbnails and Force Regenerate Thumbnails.

I have not tested: use a media management plugin instead of the media library
I note that the function for generating the thumbnails of the PDF files has stopped working when the theme is no longer maintained and the PHP version is the same. Only the version of WordPress has changed

[codekraft]

Maybe this is related to ghostscript and ImageMagick 6 - policy.xml?

• make sure to update Ghostscript >=9.24
• you need to search for this file /etc/ImageMagick-6/policy.xml and uncomment the pdf line

Pdf preview image generation was disabled before ImageMagick 7.0.6 because has security implications ​https://imagemagick.org/script/security-policy.php