As what its name suggests, PDFSearches is a browser add-on where you can supposedly search for documents or PDF files on the web quickly. This add-on can also convert your document files to various formats. However, be wary because its goal is to actually hijack your browser by attempting to commandeer your browser search and homepage to portal.pdf-searches.com. This browser hijacker will send you to malicious websites to get money from you or infect your computer further. It may also prevent you from changing your settings back.
Browser redirects happen because the PDFSearches software is usually installed and bundled unknowingly. Remove it immediately.