macOS High Sierra Patcher application is intended for those with unsupported Macs and Hackintosh users, but any Mac user can use the app to be able to download the complete installer file from Apple servers.
Note: Make sure SIP is disabled on the system you intend to install High Sierra on. If it's not or you're unsure, just boot into your Recovery partition of your currently installed copy of OS X, open Terminal, and run "csrutil disable". Please also note that SIP MUST remain disabled for as long as you run High Sierra. You will be warned and prompted to re-disable it if it does somehow become enabled.