A system and method for automatically extracting relevant key concepts from a free-text document and indexing the document using the extracted key concepts. The indexing mechanism applies syntactic and semantic filters to filter out irrelevant terms. The remaining terms are deemed to be key concepts for the free-text document. An input search query is compared against the key concepts extracted for the free-text document for determining whether the document satisfies the query. Prior to applying the search query, additional scenario-specific terms are added to the search query in order to improve retrieval performance. The query expansion mechanism generates a list of candidate expansion concepts, filters the list of candidate expansion concepts based on a user-entered scenario concept, and expands the input query based on the candidate expansion concepts remaining after the filtering process.