Hi Puckandme,
Thank you for participating in the Apple Support Communities. If you are receiving a blocked plug-in error, here are steps to help:
Since some Adobe products like Acrobat are no longer supported, this may be the plug-in being referred to. To correct this, locate another *.pdf file on your Mac, right-click the document and choose “Get Info”. Make sure that “Open With” is set to the Preview app. See if you still get the error message now. If you do, please continue below:
1. Restart your device to see if the issue is still there: Shut down or restart your Mac - Apple Support
2. Confirm that your device is using the most recent software to rule out the older one: Update macOS on Mac - Apple Support
3. Try the steps here to see if they help: If Safari on Mac doesn't open a webpage or isn’t working as expected - Apple Support
4. Contact Apple Support here if you need further support: Contact - Official Apple Support
Have a great day.