Happy Friday, griffithassociat!
Which software version are you running on your S8+? What's the exact error message that you receive? Since the update, have you restarted your phone to see if that helps?
Hey there! Just wondering if you had a chance to check out the suggestion above- also if you've already restarted your phone, you might want to see if you have an app specifically to open the PDF files:
Google Play Store
Search for "Google PDF Viewer"
Should be the first one to pop up, make sure it states that it was made by Google
Download and install
Restart the phone
Attempt to download the file again, you should be given the option to choose the PDF Viewer to open the file
Make sure you choose "Set as default" Or "Always" (your verbiage mileage may vary based on your device)