It might be worth looking at this post. Whether it’s worth the effort must depend on how many files you need to process. It’s also possible that you could script preview to print each page back to DT individually.
As a thought experiment, the script below will open a document selected in DT with Preview and print that document back to DT page for page. It requires that you have set up a shortcut ⌘P for the Save PDF to DEVONthink 3 function of the print dialog. The disadvantage of this method is that the original page sizes will be changed to whatever the standard is for the printer which you choose and that each page will have the same name (the latter could be solved, I think).
tell application id "DNtp"
set theRecords to selected records
repeat with theRecord in theRecords
set thePages to page count of theRecord
set thePath to path of theRecord as string
tell application "Preview"
open (thePath as POSIX file)
repeat with n from 1 to thePages
activate
ignoring application responses
print document in window 1 print dialog 1 with properties {copies:1, starting page:n, ending page:n, target printer:"*name_of_a_printer_on_your_system"}
end ignoring
delay 0.5
tell application "System Events"
key code 35 using command down
end tell
delay 0.5
end repeat
close the first window without saving
end tell
end repeat
end tell
Academic now that Jim has posted a solution with on-board software, but I had looked at Acrobat and it would seem the split action cannot be externally scripted (although I think it can be scripted within the batch processing mechanism using JS).
True, but for dealing with files inside a database, this could be a dangerous option to choose. Also, this requires installing a dependency.
The Automator workflow I submitted would be a simple and safe option to use.