If you mean that you're on a file:// URL and trying to save a PDF to Zotero, you changed your Chrome settings to download PDFs instead of showing them in the browser. The Zotero Connector can't run on file:// URLs.
Go to chrome://settings/content/pdfDocuments in the Chrome address bar (equivalent to settings → Privacy and security → Site settings → Additional content settings → PDF documents) and set it to "Open PDFs in Chrome" instead of "Download PDFs".
Upgrade Storage
Go to chrome://settings/content/pdfDocuments in the Chrome address bar (equivalent to settings → Privacy and security → Site settings → Additional content settings → PDF documents) and set it to "Open PDFs in Chrome" instead of "Download PDFs".
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