Define 'interacting with the file manager'.

With the built-in form, you can add a 'file upload' question that allows users to upload files. What other interaction were you considering?

I am trying to create a block that let's my client upload a file and assign it to a particular user in the concrete5 system. Only that user will be allowed to view that particular file. That is the sort of functionality I am trying to create! But by "interact with the file manager" I mean that the file the Client uploads should be viewable and edit able in the file manager. How do I know where to send the uploaded file?

I suspect the answer lies more in using advanced permissions than in the actual uploader.