Can't download PDF files
As of today, when I tried to download my UPS invoice as a PDF file, I was told 'could not download PDF file'. WHAT?? It normally downloads to Dropbox
MacBook Pro 15″, macOS 10.13
I would contact the vendor sending you those invoices. Ask them if they have changed how they are distributing the emails.
http://www.ups.com/ allows you to manage on a web browser all your UPS account activity.
You may want to use a newer web browser if you are still using High Sierra.