Storing UTF-8 XML using Word's CustomXMLPart or any other supported way

Question

I am writing a Word add-in which is supposed to store some own XML data per document using Word object model and its CustomXMLPart. The problem I am now facing is the lack of IStream-like functionality for reading/writing XML to/from a CustomXMLPart. It only provides BSTR interface and I am puzzled how to handle UTF-8 XMLs with BSTRs. To my understanding an UTF-8 XML file should really never have to undergo this sort of Unicode conversion. I am not sure what to expect as a result here.

Is there another way of using Word automation interfaces to store arbitrary custom information inside a DOCX file?

Answer 1

The "package" is an OPC document (Open Packaging Convention), which is basically a structured zip folder with a different extension (e.g. .pptx, .docx, .xps, etc.). You can get that file in stream and manipulate it any which way you like - but not artibitrarily. It will not be recognized as valid docx if you put things in the wrong places (not just xml elements, but also files in the folders inside the zip file). But if you're just talking "artibitrary" meaning CustomXMLPart, then that's okay.

This is a good kicker page to learn more about the Open XML SDK and if you're up to it, which allows for somewhat easier access to the file formats than using (.NET) System.IO.Packaging or a third-party zip library. To go deeper, grab the eBook (free) Open XML Explained.

With the Open XML SDK (again, this can all be done without the SDK) in .NET, this is what you'll want to do: How to: Insert Custom XML to an Office Open XML Package by Using the Open XML API.