Hello,

I get the same problem with pdf display. There has been a modification of the functioning of ImageMagick (or external Image-Magick) on the server : it won't build any thumbnail for any non-image file "for safety reasons". There is an option to do so, but it is now disabled by default. In theory, it could be re-enabled.
I asked for it, but my hosting provider refused to do so (it's shared hosting).

I found a solution for my pdf : I create a picture of the first page and upload it to the site via the Photo update plugin, but it is a partial solution : it won't work for the square thumbnails of the carrousel, which show only an interrogation mark.

Plugin is here : https://piwigo.org/ext/extension_view.php?eid=566

Hi all,
A fix for this was comitted on github, I have published a new version of bootstrap darkroom that should fix this problem