The plugin is simple to install:
upload-widget.zip and unzip it into the /wp-content/plugins/ folder.With the field "Authorized WP Role" you choose which role is allowed to upload files. Only this role and admin see this widget to upload files. Upload Widget is multi-widget, you have to create so much of widget that of roles authorized to download. Set the correct "Authorized WP Role" for each widget. Every role will see only his widget. The admin will be the only one to see all the widgets.