The Fibery API is designed to allow you to query and update the contents of a Fibery workspace. As you say, this includes uploading an downloading files.
If you want to create files, this is something that you would need to do externally. There are no doubt lots of services which have APIs for making files from source data, or you could write your own.
Within Fibery automations, it is possible to create PDF files as attachments to an entity, but that is the only format supported.