The Search box in the title bar allows you to search and find text in the active/current document.  

In a second step, you can replace the found text with a new text.  

Search

1. Open the document you want to search (single-page view)
2. Go to the Title bar > Search text
3. Enter the text or phrase you want to locate
4. Click on the Search button  or press Enter
5. The search results are displayed in the Properties panel (you are now in searching mode).
   It shows you the number of instances and the list of results within context.  In the single page view, the instances are highlighted in yellow. 

Replace

1. Enter your new text in the Replace field
2. Select the instance in which you want to replace text.  Click on Replace
3. To update all instances at once, click on Replace all

Note: the searching mode does not allow selecting text. To select text, exit the searching mode by closing the Properties panel