1. In your project, right click a folder from a read only addon like ArmaReforger.
2. Click "Transfer" and confirm.
3. The transfer operation will run as indicated by the bar in the top right corner, but it will only replicate the folder structure without copying any files.

I don't think this is intentional, at least MarioE wrote in Discord at some point that this should be working.
Transfers from my own addons works correctly.