To teach, teacher needs help for sharing these educational documents, and especially his knowledge. We present an approach to overcome the difficulty of sharing educational materials and facilitate access to content; we describe semantically these documents to make them accessible and available to different users. The main idea in our annotation approach is based on: (1) Identify key words in a document, to have a good presentation of the document, we extract the candidate words by applying a weighting process and another process using similarity measure, These keywords candidates are reconciled with ontology to determine the appropriate concepts. (2) As document reference generally other documents, we propagate the annotations of references for citing document. (3) A process of validation will be applied each time an annotation is added in order to keep the coherence of the base of annotation. After evaluation with several types of pedagogic documents, our approach achieved a good performance; this suggests that teachers can be greatly helped for the semantic annotation of their pedagogical documents.