This paper proposes a tool to automatically enrich webpages with semantic information by annotating keywords in the document with microdata markup. There are two case studies described and implemented in this paper. The first case study focuses on generating new webpages with microdata model and the second case study focuses on enriching existing webpages with microdata model. This paper also demonstrates the practicality of schema.org vocabulary as a base model to construct a referenced ontology and shows how the reference ontology can be used as a resource for automatically extracting important words and phrases in the webpages. Finally, a comparative study is conducted and the results show that the proposed approach is more reliable in terms of performance and flexibility compared to other existing automatic microdata annotations tools.