As discussed in the Object and Metadata Configuration section in the 24Files Manager Configuration, it is possible to automatically transfer documents uploaded to Notes and Attachments to 24Files (and SharePoint).
In case you do not use this feature and you still want to upload documents from Notes and Attachments to 24Files, this can be done via a simple drag & drop. Documents will be uploaded to 24Files, the documents will not be automatically deleted in Notes and Attachments.