Hi Lisaintrouble,
Welcome to Apple Support Communities. We understand that you're having an issue with opening PDFs in Chrome. We'd like to help.
Which IOS version are you running on your iPhone 12 Pro? Did you notice if this issue started after the last update or was it before? Have you attempted to open these PDFs to see if this issue is isolated to the browser? This would be a good starting point as you still should be able to view the PDF without downloading it first.
You can also try to do this to view instead of downloading: Read PDF documents in Books on iPhone - Apple Support
Keep us updated and we'll continue from there.