This tutorial teaches how to build a WhatsApp chatbot that can retrieve information from a PDF document, using the Twilio Programmable Messaging API for message handling, LangChain and OpenAI API to process PDFs, generate and store document embeddings, and select models to respond to user queries based on the document's content. The chatbot is built using Node.js, Express.js, and various libraries such as Twilio, LangChain, OpenAI, and Hnswlib-node.