To join the publication service of the Official Journal of the Generalitat of Catalonia (DOGC), you must do so through the Interadministrative Collaboration Platform (PCI).
The PCI has a generic messaging for all the services of the AOC Consortium, therefore, you also need its documentation, which you can find in the FAQ Generic documentation to integrate with the PCI .
You also have documentation and information about the integration with the DOGC service .