Apologies but the documentation is currently incorrect, and why its not working, including the "explore this API" functionality.
The sequence should be :
1. Call filing history (as above)
2. Call document api for transaction you are interested in.
2.1 The document API returns a 302 Moved response with a Location: header pointing at the document
3. Get document by following the Location: URL. This can only be done once, without repeating 2, and must be done within a short time window, before it expires.
The following forum post provides further information which maybe of assistance.