All necessary documents must be legalized. Transcript, letters, diploma, etc. they all must be signed by school authority.

All documents must be notarized by a notary in the county where the school is located. Sometimes there’s a notary at the same school. Otherwise, this should be done by an external notary.

In some states the notary's signature must be recognized by the county clerk. In some cases, this step is not necessary because the Secretary of State office directly recognizes the notary's authority. To determine whether this is needed, it’s best to directly call in advance the Secretary of State of the corresponding state and ask the question if this is needed to get the Apostille of the Hague of academic documents.