Most of my Word knowledge & programming skills are self taught, developed whilst helping other users solve their Word productivity issues. Consequently, I can't point to a textbook I've found useful for learning this stuff.

A book you might find useful is The Secret Life of Word: A Professional Writer's Guide to Microsoft Word Automation, by R Delwood, published by XML Press in 2011(http://xmlpress.net/publications/word-secrets/). I contributed content for and did much of the technical review of this book. This isn't a programming book as such (though it does have some programming in it) and doesn't profess to teach you how to program. Rather, it shows how to combine Word's various tools to achieve whatever the desired result might be. Another that I contributed to (and has much more programming in it) is Word Hacks, by A Savikas, published by O'Reilly Media in 2005 (http://shop.oreilly.com/product/9780596004934.do). I contributed content for this book also. Although it pre-dates Office 2007, much of the content is still relevant.

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Cheers,
Paul Edstein
[Fmr MS MVP - Word]