Thanks Fumei....

As I suspected, the same process seems to be fired by DC or RMC+Open.

So I'll rephrase the original question: When in Document_Open, can I look at some system variable to determine what method was used to open the document?

I strongly suspect the answer is "No".

As to the next bit, I currently have VBA in Document_Open which immediately shows an Userform etc. So from then on, processing is restricted to options offered to the User.
To amend/update the code, I normally access the document's VBA by opening the document, then use Alt+F11, but the above restrictions mean that option is no longer available to me.
Therefore, at the moment in Document_Open I detect the current User's name, then, for selected Users (me!), I offer the option of normal processing or VBA access.

I was just musing on the idea of simplifying this process....