Does the 'manual' for Quest exist in downloadable and printable pdf format? I have done a search of the forums and elsewhere and the only references to the existence of such a thing seem to be from 2004 and the links are now dead.

I know of no manual. Here is the latest code on GitHub.
https://github.com/textadventures/quest/releases/tag/5.8.0-beta.0

I was beginning to suspect as much. Thanks for the link.

There is this. It explains much of Quest.
http://docs.textadventures.co.uk/