From the site:
“Find thousands of Public Domain files available for you to download and use, completely free of charge. Our goal is to build the largest collection of available files from all over the web, consolidated into one fast, easy to search archive.”
From the FAQ:
" What are sponsored files?
To help cover the cost of hosting our site, we may include “sponsored files” in our search results. Sponsored files are provided by 3rd party companies, and may require payment or registration to use the file. Additionally, sponsored files may NOT be in the public domain."