Add the files to your Media Library. The media library will give you a link to the files. Then make posts with the name of the file for title and a link to the media library created link to the path for your file in it. Now the default WP search widget will find the posts, user can click the link in the post and download the file. If you want control over who can download you can make the posts private for the ones you only want approved users to access. Anything more than that will require php and/or plugin.
