On the Eurail timetable, InterCity trains are listed as "IC". These trains require a reservation, which can only be made at a train station in Portugal. Reservations are not required for regional trains and commuter trains. These trains have no abbreviation in the Eurail timetable.
On the Eurail timetable Alfa Pendular is listed as "IC". On the CP website you will find it listed as "AP". This train requires a reservation, which can only be made in Portugal. A reservation is not required for the Celta train, listed on the Eurail time table as "ARC".