The Devonthink “Help” menu item contains links to full documentation.
But it’s not searchable unless I download it as an independent PDF file first. (The only way to download it seems to be from a specific page, https://www.devontechnologies.com/support/download/extras . It can’t be downloaded directly from the Help menu.)
For example, searching for terms like “replicant” or “duplicate” gives zero results. Of course both terms actually occur in the documentation multiple times.