Can I protect/add passwords to a Word document using SDK 2.0?
No. The current design of the SDK cannot decode an encrypted OOXML package or add passwords to/encrypt OOXML documents. You may leverage automation or server-side service to implement this requirement or refer to System.IO.Packaging. Open XML SDK only support features to protect a document such as preventing the sheet from being edited in UI. For detailed information, please refer to: forum discussion thread.