what is the difference between legal notions of An estoppel certificate , and Apostille?

They are not in any way similar. An estoppel certificate is generally used by the buyer of a building or mortgage to obtain assurances regarding other existing tenancies and mortgages on the building. An apostille is a certificate by a federal government official that the notary taking an acknowledgement is authorized to do so. It is used to record or use the document in another country.