Attachments option allows to add and download additional files to the design selected. User with permissions to edit and/or export designs will have this option available. Once the option is enabled in Administration, you will see a new button 'Attachments' available on the bottom menu.
1. Select one design and click on the button 'Attachments' and choose 'Add Attachment...'
2. In the new dialog upload the attachment.
3. Once uploaded the file is attached and you or other with permissions will be able to download it.