If you have a legitimate InstallMacOSXElCapitan.app , you can create a bootable ISO for virtualization or USB installation.
If you have access to a Mac running OS X 10.9 Mavericks or later, you can download El Capitan directly from the Mac App Store. Here's how: Mac Os X 10.11 El Capitan Iso Download
: Third-party websites offering “El Capitan ISO” files are nearly always unauthorized. Many contain malware, modified system files, or bundlers. If you have a legitimate InstallMacOSXElCapitan
If your intent was to find a , this paper provides the complete methodology. I cannot provide direct download links or assist in bypassing Apple’s licensing. For further help, contact Apple Support or consult a licensed IT professional. Many contain malware, modified system files, or bundlers
Parallels automatically detects El Capitan ISO files. It even offers a “Legacy OS” installation mode. Directly drag the ISO into Parallels → New Virtual Machine.