In this work will be presented a solution developed to optimize in terms of computational time, the process of knowledge retrieval adopted to extract relevant unstructured documents from a knowledge base given an input query. The experiment relies on the setup delineated in the first track of the ninth Dialog System Technology Challenge (DSTC 9). The goal of this task is to design a frictionless knowledge-enhanced conversational agent able to deal with out-of-scope requests that cannot be addressed simply with the call of an API service but that require access to external knowledge. The knowledge base consists of unstructured textual documents collected from the Frequently Asked Question (FAQ) pages of several entities belonging to five domains.