Yes, you must have a ticket to access each screening of the Festival, the Immersive Competition, and the parallel sections (Quinzaine des Cinéastes, Semaine de la Critique, ACID et Cannes Cinéma).
Tickets must be reserved via the online ticketing website.
If you do not obtain a ticket for the screening you want, you may try the last-minute access queue, with your badge.
See : "How can I see a film if I didn't get a ticket?"
Press accreditation holders must also reserve tickets for all screenings they wish to attend.