Hi I am Zotero and Obsidian user. I use a
simple Zotero translator that creates a markdown link to your Zotero Item when quick copying (drag and dropping) the item into obsidian.
You could find the link here Zotero best practices
Can you open the pdf from Zotero and the problem arise only when you are using Obsidain?
In my case I don’t link to pdf, but to Zotero bibliographic entry containing that item, for example
[van der Plas. 2020. Entraining neurons via noninvasive electric stimulation improves cognition](zotero://select/items/1_946JX82F)