Using the advanced search or smart groups you can filter out almost anything from your accumulated knowledge in DEVONthink. Out of the box you can e.g. get a list of all PDF documents in your database, or of all images. The selection here is not very granular, though. But you can easily locate documents using their file name. To find documents of a type not genuinely known to DEVONthink, say like Excel files, choose “Filename ends in … xlsx”. While the title of a document doesn’t show the file name extension that OS X needs to identify its type, the file name on your hard drive does.