The original plugin is at https://wordpress.org/plugins/wp-file-search/ and it provided:

WP FILE SEARCH adds a powerful feature at the search mechanism of your site, as it enables searching on the content of the files that are uploaded to the WordPress media library. The only thing you have to do is to install the plugin and it will automatically be incorporated with the WordPress default search mechanism, in order to list not only the pages and articles, but also all the files that contain a specific key-word.

Change log:

1.0.2

Added search of the file format .DOC.

1.0.1   Download from https://kernl.us/api/v1/archive/5835b5dcb2c6b63167fb5eb8

Fixed a conflict on the class Parser with another plugin.

1.0.0

File formats added to the standard Word Press formats are . ODT, .DOCX, and PDF.