A search engine is just a service in your application that lets you search for related keyword (sentence or word) in your application's data; data sources such as databases based on what you already have.
You can write the code to define this logic inside your application. If you need guidance, you can read this article of mine to learn how to create the functionality of search inside your application in ASP.NET. Article would guide you through the rest of the implementations and a security tip for SQL Injection.
How to search for related query inside the Database using ASP.NET[
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