Laserfiche itself is pretty agnostic about the file types that it can work with. There are a few exceptions, such as images, office documents, or PDFs, but for the most part, you can attach anything. To my knowledge, there isn't a setting in the repository that would restrict specific file types.
I would recommend using workflow to do some vetting on documents that are added. You can do it two a couple of different ways. If you have a specific place that users scan into, say an intake folder, you can add some simple checks into existing workflows to check if an edoc exists, and then check the file extension. The Download Electronic Document activity returns an extension token.
Another option is that you can setup a scheduled workflow that does searches for new documents that have an electronic document, and then loop through them checking for file extensions. The For Each Entry activity can return an extension token.