When creating OpenPGP subkeys, the master key signs and certifies that a subkey belongs to that master key. Can be used master key to decrypt something encrypted using an encryption subkey? I guess not, but I want to be completely sure. Am I right or I missunderstood?
The OpenPGP primary key and subkeys are cryptographically different keys and simply bound to each other by special signatures defined by the OpenPGP protocol. They cannot be used to decrypt information encrypted for the other one.
This also implies you should never completely delete your old (encryption) subkeys but simply revoke them; otherwise you'll lose access to your old encrypted documents and messages.