The Myth of Windows 7 Service Pack 3: Why It Never Arrived
You must have the April 2015 Servicing Stack Update (KB3020369) installed first. windows 7 service pack 3 iso file download link
Since an official SP3 does not exist, nearly every website offering a "Windows 7 SP3 ISO download link" is a trap. Here is what those files usually contain: The Myth of Windows 7 Service Pack 3:
This was the first and only official service pack released by Microsoft for Windows 7, launched in February 2011. Some users use tools like Heidoc
Some users use tools like Heidoc.net's ISO Downloader or MajorGeeks to find original images, but these are unofficial and should be used with caution.
You download a clean, official Windows 7 SP1 ISO, and use the Simplix tool to hot-stream all remaining updates directly into the installation media. How to Create Your Own Updated Windows 7 ISO
The final service pack for Windows 7 is Service Pack 1 (SP1) , released on February 22, 2011. Any website, forum, or torrent claiming to offer a "Windows 7 SP3 ISO" is distributing unauthorized, unofficial, and potentially dangerous software.