Hope you are doing well. Per the description, I understand that you want to change your default printer to an Adobe PDF printer.
The option to create Adobe PDF is available on the desktop version of the application, as it requires installing plugins. Mobile devices have certain limitations when adding additional plugins to the application.
What you can do here is, go to the print option, click on export on the top right, -> save to files this will create a new copy of the PDF to your internal storage.