[Edit: The following in Italics is mistaken.
I'm not sure this can be done simply.
I believe that in earlier versions, the vba command

Code:

Options.SavePropertiesPrompt = True

would do it. I do not see it having effect since the disappearance of the document properties panel.

You could, I believe, intercept the save command with a userform that would query for the information and put it into document properties prior to saving. [End mistaken]


The following command, if placed in an appropriate macro should do it:
application.DisplayDocumentInformationPanel = True

While this appears to be an Application property, it does not seem to be sticky.

You could put it in an intercepting macro for Save and SaveAs commands.


For doing this with a userform take a look at Prompt to enter (custom) document property in Microsoft Word - Super User.
See also: Intercepting events like Save and Print.


sorry, I need to get to bed, early morning class I'm teaching.
[End Edit]