Hi, I`m currently doing this. This is how the flow looks like, if you have any question please do let me know.
In my case i have attachments from a legacy system that have been linked to customers. It`s a 2 step flow and it`s using context - 1st step is inserting files into SFDC (using ContentVersion object), 2nd step is quering the imported versions and adding them to a library that is being manually created in advance and sharing to all users through a Public group (Using ContentDocumentObject).
In the first part I`m reading the files from a folder, then i have two csv files where i`m doing two lookups - one for the filename and one for the customer.