Yes, you can play 4K movies on your Samsung 7 series TV from an external hard drive using USB. The Samsung 7 series TVs are capable of playing 4K video files, and you can connect an external hard drive to the USB port on the TV to access and play those files.
To play 4K movies from an external hard drive on your Samsung 7 series TV, simply connect the hard drive to the USB port on the back or side of the TV. Your TV should automatically detect the connected device, and you can then navigate to the external source or USB option in the TV's menu to access the files on the hard drive. The TV should be able to play a variety of video file formats, including 4K video files, as long as they are compatible with the TV's supported codecs and file formats.