Anyone else out there having trouble downloading a file and after unzipping and starting up, you get the message that "Obduction (what I ordered) is damaged and can't be opened. You should move it to the trash?" I've used all three browsers to download (Safari, Firefox and Chrome). This is ridiculous. I want my money back!

This may have to do with the more recent change in macOS security settings when Apple did away with the "allow apps downloaded from" anywhere option. I got the same messages for some GOG games in Sierra until I manually re-enabled the security setting. I still find it peculiar that macOS acts like an app is broken even when it isn't as may be the case here. This site explains how you can do so.

Download corruption was reported for this game was reported previously:

https://www.gog.com/forum/obduction_r/obduction_165_for_mac_unsigned_broken_menus_slower_graphics/post8

Something may be up.

If Mumbles fix doesn't help, best bet would be to follow up with GoG support. It's discussed in this thread:

https://www.gog.com/forum/obduction_r/obduction_165_for_mac_unsigned_broken_menus_slower_graphics