Import your document and export it as template, should be File -> Export -> As Template.
You can then create a new record via Data > New from Template > My Template Document
From help:
Templates are stored in the ~/Library/Application Support/DEVONthink 3/Templates.noindex folder. In order to manage your templates, rename them, organize them in subfolders, or delete them, you can quickly access this folder by selecting Data > New from Template > Open Templates Folders.