From a comment made here, I have installed a dropzone on the Add/Edit Product, Digital tab. This allows the admin to upload (and assign) digital files while creating a new product. Note: it is (probably) possible to open a new browser window, upload a file from FileManager, go back to the Add Product browser window, click Refresh File List, and select the file to assign to the product. So, I have written up the changes to the code needed to implement this. This is not an extension