Unlike standard Apple disk images ( .dmg ) or ISO files ( .iso ), .rdr files cannot be opened by default macOS tools like Disk Utility. 2. How to Open and Use a .rdr macOS Image
Create a raw, bootable disk image (close to the fictional .rdr ). download macos high sierra 10.13.5 image file -.rdr-
You double-click. The installer launches—but it's not the familiar High Sierra wizard with the globe and the progress bar. It's the old NeXTSTEP installer. Black text on a grey gradient. No images. No branding. Unlike standard Apple disk images (