Help installing pgAdmin

My name is Pedro Domingos,

I've been trying to install pgadmin on my macOS (System specs on the image bellow) and I can't run any version. 

With the last updated version it doesn't even let open the .dmg, showing a "image damaged" message (and I've tried to download it several times). With other older versions, the app installs, but then it doesn't initiate.

I wonder if you could help me with this.

Thank you!

Best regards,

Pedro Domingos.