Indeed as that’s a core requirement of a smart rule, targeting a location.
Set up a watched folder in the Finder and index it, ideally in the Global Inbox or the Inbox of a database. Then use a Move Into Database action to import the file into the database.
It would be best to use a temporal criterion, e.g., Date Added is This Hour or to use a Move action at the end to remove it form the watched group. This avoids potentially reprocessing the file.