If you look at the Microsoft Open Specification Promise it says: "Microsoft irrevocably promises not to assert any Microsoft Necessary Claims against you for m

If you look at the Microsoft Open Specification Promise it says: "Microsoft irrevocably promises not to assert any Microsoft Necessary Claims against you for making, using, selling, offering for sale, importing or distributing any implementation to the extent it conforms to a Covered Specification (“Covered Implementation”), subject to the following..." [Doesn't cover non-MSoft patents. Not surprising.] Office Binary formats are under Covered Specifications. I wouldn't use the format, but not sure it's "dangerous" to write apps that read or generate the format.