I guess you're using the latest version 5.4.6?

In LW go Tools > Options > Search. In the Search Filtering section, click on the Configure button next to 'Change the ability to search for programs'. Untick the box to allow you to search for & share programs > ok. Now click ok again on the Search page.

On that same Search page, click on the Filter File Extensions button... you'll see which extensions are being filtered & you can add more extensions to the list if you like. Just remember to click ok on that page & then also again on the Search page to save any changes