Blocked Plug-in in Safari 10.1

Without clicking the back button (or Command-[ ) of the browser:

1. Although the plugin is blocked, you can still use Command-S (or File > Save As) as well as File > Export as PDF to save the file to a folder.

Alternatively, click the back button (or Command-[ ), and then:

1. Option-click on the original link to download the file
2. Command-click opens the PDF in a new tab (PDF will not be blocked)
3. Ctrl-click yields the option "Download linked file as"

Not an answer but a clue. I am having the same problem. It started yesterday when I installed Adobe Reader DC and selected custom install and chose not to install the Adobe Reader browser extension. Before this PDFs were showing with options to open in Preview or download.