Patents must cover specific inventions. You cannot patent MS Office. You would have to identify specific inventions in MS Office. Other office software can choose to implement a different version of the feature without using that invention.
IIRC Sun released the source to StarOffice under GPL and that became OO.org.
Furthermore, member countries of the EU still retain control over their individual patent systems but there is also an EU patent office. If I want to patent something I can do it here in GB or send it to the EU or go for an international patent (PCT). These days one files a patent in the countries that they think they will sell their invention but not necessarily every country.
