Hello Dayanidhi ,

Generally , Annexure means it is a legal document which needs to be included at various points and give information about what things you need and what to do in a prescribed format or document manner .

Accordingly , KEA (Karnataka Examinations Authority ) follow some rules and regulations so , they have their own annexure  to follow . That is the reason behind using this word in document  .

I hope you understand very well .

All the best !!!!