Are you always getting redirected to the TopPDFSearch page every time you open your browser? If this happens, a browser hijacker is causing this. TopPDFSearch is found to be a browser hijacker that will attempt to commandeer your browser search and homepage towards toppdfsearch.com.
Search results from this fake search engine will send you to malicious websites to get money from you or infect your computer further. Additionally, it will monitor your browsing activities and may also prevent you from changing your settings back. TopPDFSearch is usually installed through bundled software without you knowing. You have to remove it immediately before it further damages your computer.