Yes. But where you ask? Within the Sandbox interface, you can click the Attachments Tab (located under the content item title) and either drag/drop a file into the dotted area, or click 'choose file' to browse your file system for the appropriate document.
You can also drag and drop an image from your desktop directly into the edit mode of the WYSIWYG, which will then automatically attach the image to the content item's attachment tab.
If you click the Pencil icon after attaching a file an overlay will pop giving the ability to add additional meta data to the attachment.
For more details regarding our attachments feature check out our deep dive a