How to make preview default app again?

Single-click any PDF document in the Finder. Press option+command+i to show its information panel. Find the Open with: section, and change that from Acrobat to Preview. Then click through the entire Change All… button to make Preview the default PDF opening application. Close the Show Info panel.

Select/ highlight a document, press command- i the info panel will pop up.

Go to Open With and select Preview, now press Change All.

You are welcome. That keyboard shortcut also avoids the Finder scurrying the Get Info panel (cmd+i) beneath an open browser window too.