All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad is His slave and Messenger.
Watching pornographic films is reprehensible and forbidden.
So, whoever watches them must repent to Allah Almighty and immediately stop watching them.
He should know that Allah is watching him, so he should fear His Wrath and His punishment, Glory be to Him.
However, watching them is not Kufr (disbelief) as long as the person does not believe that doing so is lawful.
Even if these films include some Islamic slogans, such as the Hijaab, it is still not Kufr.
Allah knows best.