According to Wiki, the studio version of Paperback Writer was the loudest recording The Beatles had done up to that time. The bass was also turned up in the mix in order to, as John Lennon said, sound more like Wilson Pickett records. But it's the vocals that we care most about: The repeated chorus we first encounter in the song's introduction sounds as if the three voices were double tracked. It's also possible they used vocal triple tracking as they'd done on Because.
But here, they do what they can with just the three.
Note: I've reposted the video. What I posted previously apparently no longer exists. This version appears to be of a lesser quality but you get the idea. The entire Tokyo concert can be seen here.
An impressive display of skill especially when considering the often lackluster results of other bands who try to ape the complicated arrangements of their recorded versions (Bohemian Rhapsody leaps to mind). It's also a testament to how tight and polished this band could be (even with Paul's errant mike). The dues paid in their early days playing the clubs show well here. They don't even appear to be breaking a sweat: Note how John tries to make George laugh. Even with the distractions of a screaming audience it takes no toll on the quality of their performance.
Another reminder of the shame that their performance career was so brief. (The Let It Be movie being another glaring example.) The lads had no equals.