Please note that Google Chrome is aware of an issue where PDFs don't open for some Chrome 78 users.
Google has posted the following:
You can normally open PDFs automatically in Chrome by clicking on the file you want to see. If your PDFs are downloading instead of opening automatically in Chrome, Chrome PDF viewer could be turned off.
Open PDFs in Chrome
- On your computer, open Chrome.
- At the top right, click More Settings.
- At the bottom, click Advanced.
- Under "Privacy and security," click Site settings.
- Near the bottom, click PDF documents.
- Turn off Download PDF files instead of automatically opening them in Chrome.
Chrome will now open PDFs automatically when you click them.