In this paper, we propose a document retrieval system based on natural language processing of documents and queries. We use single terms and term groups as indexing elements to represent documents and queries. The model is formally expressed within the Dempster-Shafer Theory of Evidence. We discuss in detail how we use this theory to represent a document collection, indexing elements, documents and queries. The retrieval function is derived directly from the underlying theory. We then present an implementation of the model. The experimental work carried out is reported last.