Thanks!

I managed to get something that works, in the end.

I couldn't access the Greg Maxey site as my firm's web blocker decided it was "military content". Turns out he mentions his old US Navy rank and that was enough to upset the filter, which seems to be set on a hair-trigger! By the time our IT chap got that fixed, I'd sussed doing it using content controls using other web resources as guides.

What I've done is create one text content control called DocNumEntry, set to editable, and multiple others call DocNumEcho, set to not editable. Then using the app Word 2007 Content Control Toolkit I enter XML thingies for DocNumEntry and DocNumEcho and link them by dragging from one pane to the other in the toolkit. Whatever that is doing in XML (which might as well be Greek to me) it seems to work - you type a document number in the DocNumEntry content control and it automatically appears in the non-editable DocNumEcho controls too. As long as I stick to the steps laid out in the tutorial example I'm using, it doesn't matter that I don't really understand the nitty-gritty.

(Unless I manage to break it, that is, when I'd be well and truly buggered!)

All of which is a long-winded way of saying I think it's all sorted now.