When I press the super key and search for a pdf (or a LibreOffice document) and then click it to open, it opens in gnome-documents. Which while I'm sure is well intentioned is very frustrating, as it's a piece of incomplete software. When I click on a document I want to work with it not just look at it (and sometimes that's not even possible).
Edit: Instead of using the extension below I also discovered if you type more of the name of what you are searching for, it will display a "Files" section with a duplicate result and if you click this result instead, it will open the appropriate application.
Also, regarding the Documents search results, if you really want to you can remove the search provider and only use the Files search provider, which does as you wish. To remove the Documents provider:
sudo apt-get remove gnome-shell-search-provider-documents
and if you don't already have the Files provider installed:
sudo apt-get install gnome-shell-search-provider-nautilus
The best solution to this, at the moment the only solution I know of, is to use the Tracker Search extension:
This works with iirc 3.2 and 3.4 and integrates the search results from tracker into the overview. With this method you would then look for the tracker results and click it instead of the "Documents" results which opens Documents.
The Documents search provider is responsible for why it doesn't open Evince, as it was designed to show the results of Documents in the overview. Although I'm not sure if it is actually a search provider, it may be more integrated than that.