Can someone decrypt my files without my knowledge?

You’re in control of who can decrypt your files. If you don’t give access to anyone, only you can open your encrypted files with your master password.

If you give access to specific users through the NordLocker application, they will be able to decrypt your shared files with their master passwords. 

NordLocker has zero knowledge about your data, so there’s no way we could access the content of your files.