I understand you're looking for a free download of Mac OS X El Capitan 10.11.6 ISO.
Apple Support Webpage: You can download the full InstallMacOSX.dmg (approximately 6.2GB) directly from the Apple Support website. mac os x el capitan 1011 6 iso download gratis work
Run the .pkg: Run the installer inside; this will place the "Install OS X El Capitan" app in your Applications folder. I understand you're looking for a free download
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Extract InstallESD.dmg: Use a tool like 7-Zip to look inside the .pkg file and find InstallESD.dmg.