Critical fixes for vulnerabilities that existed in earlier 10.13 iterations. What is an "RDR Exclusive" Image File?
If you specifically need version 10.13.5 and are already running a lower version of High Sierra (like 10.13.4), you can download the manual update files: macOS High Sierra 10.13.5 Update macOS High Sierra 10.13.5 Combo Update (recommended if you are several versions behind) Apple Support Important Considerations how to upgrade to macOS High Sierra 10.13 - Apple Community download macos high sierra 10135 image file rdr exclusive