The Mendix Deployment Archive (.mda) you create for deployment contains the model (and Java codebase) that is run on the server. You could open this file as it is basically a .zip file and look at the contents (mainly the model).
However I doubt this will provide any useful documentation to the client, my recommendation would be to use the documentation fields available in Mendix and use the Export documentation feature (App Explorer > Right click on App 'ProjectName' > Export Documentation) . This will create documentation for all the project documents and its added information (the domain models, logic: nanoflows, microflows, java and javascript actions, the annotations and documentation fields)