You probably arrived here looking for the NGSIv2 Specification document :)
Instead of that, you should use the Orion API Specification, which is based in the original NGSIv2 specification but including all Orion improvements and enhancements built upon it. In addition, it is a more up to date, accurate, comprehensive and navigable reference. Enjoy it!
However, if you are still looking the old NGSIv2 documents, they are available here: