Open XML Format SDK April CTP
Download here. Class Diagram. What's new? Roadmap.
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I see Erika also has a link to this video of Eric White discussing the SDK with Zeyad Rajabi. Zeyad shows (@ approx 5'00) an example of "injecting" an xml data fragement into an existing OpenXML document to change the contents - in effect the programatic equivalent of an XML mail merge.
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