Hi Pieter,
Looking at the Importer Microflow, you need an object of the Generalised System.FileDocument. Use the CommunityCommons Base64Encode to create a string (unlimited) in your domain model. The Base64Decode can be used to populate the Generalised System.FileDocument object.
I think you will need a new widget that takes in a file from a filesystem and returns the Base64encoded string. Maybe this could work https://marketplace.mendix.com/link/component/208170 or you need to build it yourself
Go Make IT
Thanks so much Marco. I will attempt this and inform whether i was successful :-)