While Automator is not specifically supported in DEVONthink 3, it doesn’t mean it can’t be used with DEVONthink at all. As is discussed in the Help > Documentation > Automation > Automator section, you can still use the Run AppleScript command for some integration.
Here is an example workflow for splitting PDFs showing a DEVONthink-to-Finder and a Finder-to-DEVONthink integration…
DT Split PDF.workflow.zip (270.3 KB)
You can put this workflow in the ~/Library/Application Scripts/com.devon-technologies.think3/Menu directory to run on selected PDFs, if desired.