There might be another name for Zoom Indexer at the WP Search Plugins [wordpress.org] directory because I couldn't find it there, but there are many other search plugins to choose from. Some offer specialized search options.
It is important to only use plugins from wordpress.org to ensure their compliance because plugins have full access to your core files, an easy route for abuse.
How to create a search engine for your WordPress site wrensoft.com/zoom/support/tutorial_wordpress.html (not affiliated with Zoom. Just happen to have used their software on a number of traditional HTML sites)