Indeed, you have no access to the source code and thus can not edit the application. It is licensed as proprietary software (see for example What is proprietary software and how does it work? on what this entails).
If you download a Desktop version the code-base is similar to what the Cloud and Server editions have except that the latter two have additional code for multi-user use and authorizations. You can not edit the Desktop nor any other edition as the code is kept secret by the owner.