macOS will say it's damaged. It isn't.
I just don't want to pay 99$ a year to Apple so the message shows for any app whose developer hasn't paid Apple's yearly fee. Opening it the first time takes three steps, and you only do them once.
- Drag PaperStack into Applications, then double-click it once and let it fail.
- Open System Settings → Privacy & Security and scroll down to Security.
- Beside the message about PaperStack, click Open Anyway.
Or build it yourself
It's the same code but needs Node, Rust and the Xcode command line tools.
# clone, install, build straight into /Applications
git clone https://github.com/Antonio-Leitao/paperstack.git
cd paperstack
npm install
npm run install:local