Basically, documents in DOC² are classified/defined via AI and Regex. However, there a few exceptions, you need an additional negative filter (exception filter) that allows you to exclude certain things. Exception filters are important to achieve the best results.
To define an exception filter, open document view for any document:
There you have the option of calling up the exception filters via the "Exception Filters" button:
You can then set the appropriate filters and apply them via "Apply":