You don't need a pem file for staking/delegating.
PEM is basically just an unencrypted form of the json file you already have.
There is no difference in things you can do with one or another.
If you are talking about validatorKeys (which need to be pem's) the above documentation would be helpful to you and you would learn how to generate a pem for your validator.
Note though, that the validatorKey.pem is seperate from your wallet and doesn't hold any coins.
Also running a validator node requires you to own 2500 egld and to have the technical knowledge to do, as well as a hosting provider that allows crypto and a server with enough power.