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

Searching for a often leads users to specific communities like "ihackinOS" on GitHub or Hackintosh forums. While macOS typically uses .dmg or .pkg files, the .rdr format is a proprietary disk image often used for "Ready-to-Restore" installations that include pre-configured settings like EFI folders for specific hardware.

: 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)

: Formats developed by R-Tools Technology (R-Drive Image) for system recovery and hard disk imaging. Official vs. Unofficial Downloads

: You can find various macOS High Sierra images, including ISO formats , which are useful for virtual machines. How to Use an .rdr Image File

: Projects like ihackinOS/MacOS-Collection host various versions, including .rdr files meant for quick restoration.

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

For the highest security, you should prioritize official Apple sources. However, because 10.13.5 is an older version, finding the exact point release can be difficult. 1. Official Apple Channels (Recommended)