DEVONthink Pro (Office) lets you save files directly to the database using the watched Inbox folder. This folder is deeply buried in your Library folder but added to the Finder sidebar for easy access. It also appears in Open and Save dialog windows.
Don’t use this folder for e.g. saving a document from Microsoft Word and continuing to work on it. As the document is, after a short delay, moved to the database, Word will fail saving your changes afterwards. Better save the file to your Desktop first and move it to the Inbox in the Finder sidebar when you’re done for now. Re-open it out of DEVONthink when you need it again, e.g. for making more changes.
BTW: Some applications notice when the document is moved and handle this properly. But that’s solely up to that application, not DEVONthink.