.then(function(){
    return page.keyboard.down('Control')
})
.then(function(){
    return page.keyboard.press('A',{delay:100})
})
.then(function(){
    return page.keyboard.press('V',{delay:100})
})
.then(function(){
    return page.keyboard.up('Control')
})

I've tried page.evaluate( () => document.execCommand( 'selectall', false, null ) ); and it works. But how to cut and paste after that?