High Sierra download "Damaged"in App Store

What's happened is that the App Store previously fed you a copy of the 10.13 High Sierra installer into your Applications folder that needs to be deleted and trashed before you can download a fresh working copy from the App Store now. Whenever you try to download a new one it sees you already has one (even though it's broken) and won't override it. Be sure to check your applications folder, it would be called "Install 10.13 High Sierra" or something similar, and it would be 4GB+ in size.

If, for any reason you aren't seeing that. Just upgrade to 10.11 El Capitan first.

https://support.apple.com/en-us/HT206886

Step #4 contains an El Capitan disk image install creator. Open it to mount the image automatically, run the package contained inside the image, and the pacakage creates an El Capitan installer and places it in your Applications folder that you can then run to do the El Capitan upgrade. A fresh High Sierra download from the App store would probably download and install fine once you are on El Capitan.

Hi Richard, here is a link that gives you access to pretty much all the Mac downloads you could ever want. It's a great link to keep in mind, now and down the road. Specifically, with respect to your question, here's how you upgrade to Mac OS High Sierra. The technical requirements for High Sierra are listed there and broken out again here. (As a general matter, it's always good to reconfirm that you meet all the requirements.)

As noted in the "upgrade to High Sierra" link, you like also have the option of upgrading to the most current version of Mac OS, Mac OS 10.15.X (Catalina). But if High Sierra is what you are after (perhaps because of software compatibility issues or for other reasons), the link just given will take you where you need to go. If for some reason you still encounter difficulties, you can go direct to the source and upgrade to High Sierra 10.13.6 directly by using the combo updater.

To paraphrase Led Zeppelin, "... there are [at least] two paths you can go by, but in the long run, [although] there's still time to change the road you're on," you likely won't need to. Not at this point and for this reason, at least. ;-)

Good luck!

-- JDee

Don't use Firefox for this link...

https://itunes.apple.com/app/macos-high-sierra/id1246284741?mt=12

If you get a corrupted message...

Naw, not damaged, it's just that you have an old copy already in Applications, there are 2 cures...

Disconnect from the Internet & set the Date back to 2014, then you can run the Install MacsOS High Sierra App in Applications, so expired Certificates are not expired.

Or... trash the Install MacsOS High Sierra.app in Applications then a new copy more recent version can be downloaded.