If you want the search to be flexible like handling things like root stemming (i.e. for matching words that are pluralized etc) you might want to put the text into an Elasticsearch database.
You might run into problems with the field length if these are long documents. A possible solution to that would be an putting each page into its own field inside of the document.
If this is for a non tech user to search, the Kibana interface should be relatively easy for anyone to use.
Likely that the browser they were pointed at went missing (executable moved or something), or was crashing at launch, and this is just Windows saying "I can't find the default you wanted so I am falling back to Edge, otherwise a lot of stuff is going to be broken".