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.
"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.