: You can often find High Sierra through a direct App Store link that may not appear in standard searches.

The .rdr extension is not a native Apple format. In the context of macOS downloads, it usually refers to one of two things:

If you specifically need a pre-imaged file (like an .rdr ), these are typically hosted on community sites:

Below is a guide on where to find these files, what the .rdr format entails, and how to safely install macOS High Sierra. Understanding the .rdr File Extension

: If you already have an earlier version of High Sierra, you can download the macOS High Sierra 10.13.5 Update directly from Apple Support to upgrade your system. 2. Community Repositories (.rdr and ISO)