Cause B – CORS Issue: This happens a lot when users don’t understand what files access means in the modern web. PDF files are not accessible from one domain to another just like that. They require permission. You need to set proper CORS permission into the domain where the PDF files exist, so that your domain can access it. NOTE: PDF files from online file-sharing servers like Google Drive, One Drive, Dropbox cannot be configured for CORS access. They won’t allow it.