Each Adobe Reader 9 window is created from window class AcrobatSDIWindow and parented by the Windows Desktop. Enumeration of child windows of this class within the Desktop window returns the exact number of open Adobe Acrobat 9 documents.
Each Adobe SDI window has a menu attached to it. It is possible to read the structure of the menu including the Ids of submenus and items.
No captions can be retrieved though -- due to the fact that the menu has substantial dynamic (run-time) building part. That part hides, shows, disables and enables items on the fly. Same, for example, as VFP shell does with its main menu.
From looking at the XML-formatted AdobeReader 9 menu structure and comparing it to the actual menu, some pretty obvious conclusions can be made.
The most important things is the menu item Ids. If the Id of a menu item is known, as well as the handle of the window hosting the menu, then the menu item can be virtually "clicked on" by calling the SendMessage with specific parameters.
= SendMessage(hWindow, WM_COMMAND, m.nItemId, 0)
The hWindow above is the handle to AdobeReader SDI window. The nItemId is a numeric value that can be recognized by this menu as a valid menu item id.
For example, passing nItemId=6019 will close the document open in the SDI window, leaving the window empty. And passing nItemId=6033 will close a given SDI window.
Still the menu item Ids are not documented, and probably change from version to version, which is a substantial obstacle when deciding to use this approach.
The AdobeReaderSDIWindow class is able to virtually "click on" an item in the main menu of Adobe Reader 9 window. This is a part of what you can do:
enumerate titles of all open Adobe documents
activate a document (the document moves to the front)
switch a document to Full Screen Mode
copy a document to the Clipboard
close a specified document or all documents
open Print Setup dialog for a document
open Print dialog for a document
You can also open a PDF document either by a file name or by invoking File Open dialog.
* * *
Jan.26, 2009: Starting with version 9 of the Adobe Reader for Windows, may be even with an earlier 8+ version, the preference "Show each document in its own window (requires restart)" is no longer available.