Annexure usage in Writing
Annexure is a common Indian-English word describing supplement or appendix to a document. (usually: legal, taxation, proposals, technical reports etc.)
You may want to use annexure when you are referring to the detailed part of the document. "For detailed 5-yr tax assessment worksheet, please refer to Annexure..."
Oxford Dictionary: annexure
PS// One can use addendum to describe additional materials or afterthought.