Hi, yes, in Confluence there is a basic search (or find) and replace command, pretty much like in Word:
Find and replace text
In the editor toolbar:
Click the search icon (the little magnifying glass) on the toolbar, or use the keyboard shortcut Ctrl+F (Windows) or Cmd+F (Mac OS).
Search matches are highlighted in yellow. You can step through the results one by one, replace the matching text strings one by one, or replace all matching strings at once. Find and replace works only within the current page.
Here you have the link to the general info by Atlassian.
Now, as you said you need to search some words in many pages, that would be across different pages or even spaces. I am afraid that this tool would not do that, just like in Word, it only works on the page you are editing or working on. There are some, slighty more complicated, solutions maybe. Please see the links at the end.
But according to individual needs, you can find lots of plug-in solutions on the Atlassian Marketplace. Here are some ideas and when you search in the Marketplace for “search and replace” or “find and replace text” you will get many different suggestions of add-ons: