Though, actually, while the website should fix their server, if you can view the PDF in your browser (e.g., because you're using Chrome or already have the intermediate certificate in your Firefox profile), this will be fixed by the same changes we're working on to avoid other attachment-download problems (anti-bot protections, etc.).
Upgrade Storage
https://www.zotero.org/support/forum_guidelines#don_t_create_redundant_threads
https://forums.zotero.org/discussion/121800/542465563#latest
https://forums.zotero.org/discussion/121801/1334126954#latest
I have tried importing the PDF file linked above:
https://www.sanidad.gob.es/estadEstudios/estadisticas/estadisticas/estMinisterio/SolicitudCMBDdocs/Serie_hist_CMBD_RAE_1997_2023.pdf
It correctly recognizes that it is a PDF file:
https://s3.amazonaws.com/zotero.org/images/forums/u265723/2kdhgo06v63b0v7wh2si.png
But after clicking on the connector button, it displays the red cross:
https://s3.amazonaws.com/zotero.org/images/forums/u265723/8e3udjg7djh8nyfu9h2u.png Saving from an arXiv PDF file works as expected, so Zotero is running and correctly recognized by the connector:
https://arxiv.org/pdf/2502.07376
https://s3.amazonaws.com/zotero.org/images/forums/u265723/3tson3qxzh9omcei8y1q.png
From the desktop app:
The Debug ID is D1921038843.
From the Connector in Firefox:
The Debug ID is D1917218763.
Zotero 7.1-beta.11+fb8b65b32 (64-bit)
Zotero Connector 5.0.151
Firefox 135.0 (64-bit)
Windows 10
https://www.zotero.org/support/kb/incomplete_cert_chain
Thank you.