Is it possible to open a PDF directly in PDF Expert when double-clicked, rather than having it open in the DTPO viewer, then clicking the Open in external editor or viewer button?
No, but assuming that PDF Expert is your default PDF app, you can open it directly with CMD-Shift-O.
I use BetterTouchTool and have a gesture defined specifically for DEVONthink. When I control-click a PDF it explicitly activates Data > Open With > PDF Expert.
Another possibility is the “Open Externally” toolbar item (assuming that PDF Expert is the default app for PDFs)
Thanks. The open externally button helps, added to my toolbar.
May check out BTT too.