A continuously updated PDF file would be a great gain

It should at least be incrementally updated with each new release, with the developer responsible for a new feature also being responsible for a brief amount of updated documentation to be included by the documentation bloke.

To some extent, this is partly done by Mike's incremental release notes, but the release notes do not usually do anything more than state the feature increment; the only documentation increment I can remember from the release notes was John's notes on the use of the Equaliser when it was first introduced in year dot. Since then - well, put it this way - I still can't figure out how the "Tweak" features work and only recently discovered the toggle between "search" and "append" in the Search feature set!
(Mind you though - half the fun of owning one of these things is the "eureka!" experience as you use it )

Small increments in the PDF document with each release would be a way to go, at least initially.

One of the few remaining Mk1 owners... #00015