It can be quite a big work, especially if you need view and edit the documents in your application. I can just give you some initial links and very basic advice.
I hope .docx would be enough for you, not .doc. Then the best option would be using Microsoft Open XML SDK.
Please see:
https://msdn.microsoft.com/en-us/library/office/bb448854.aspx,
https://www.microsoft.com/en-us/download/details.aspx?id=30425.
See also my past answers referenced in this one:
How to add Microsoft excel 15.0 object library from Add Reference in MS Visual Studio 2010.
This is another option, with one major benefit: open-source:
NPOI.
If you still had to support obsolete proprietary non-standard .doc, you would be in big trouble. However, one way to solve the problem would be using Libre Office SDK. It would be a lot of work.
Finally, I cannot miss one very basic advice: consider not using Office formats at all. Yes, the modern format is standardized, the standard is open (ECMA), but it is still based on proprietary product, Microsoft's revenue maker. Keeping closer to open-source technologies and more open standards would always be beneficial. Anyway, you decide.
—SA
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