Because WinDVD 4 is legacy software, you should look for legitimate archival sites rather than suspicious "free download" portals that may contain malware.
Finding a free download for today usually involves navigating through "abandonware" archives or digital museums, as the software was originally a paid commercial product released in May 2002 . While it is no longer supported by its current owner, Corel Corporation (which acquired InterVideo in 2006), historical versions can still be found for retro-computing enthusiasts. Where to Find InterVideo WinDVD 4 intervideo windvd 4 free download