This is solely within the desktop Zotero. It used to be that when I clicked on one of my uploaded PDFs in one of my previously made entries, it would open the PDF externally. Then one day, it was just opening the PDF in a new tab within Zotero. The error is happening in the new tab within Zotero. We have Adobe Creative Cloud here if that helps. I would prefer to email you the screenshots so I don't create a backdoor access to our files. Please send me an email address.
Can you take a screenshot of what you're seeing, upload it somewhere (e.g., Dropbox or Google Drive), and provide a link here?
Does it work if you open the PDF in this online viewer on Firefox?
Most likely this is a scanned paper with extremely large images. And is probably this issue.