Who said anything about that? That would be plagiarism, and/or cheating, to do so in an educational setting.
Complex math, being introduced into the high school setting more and more, requires enhanced tools. Basic math is being taught in an altered way to show relationships to numbers instead of doing simple equations.
Modern history has been recorded, what a better source of information than actually witnessing the first-hand account, and applying the scientific method - as should be done with history - to interpret it.
Proper Sciences would easily benefit from digital learning. Atomic weights, something I used to have memorized back in the day, could be referred to at will. Formulas can be swapped on the fly. Dissections in biology could be done digitally. Certain labs could be performed digitally as well.
English... well that's a no-brainer. In addition to digital books and instant access to a digital library; learning the language with a tool that has instant access to dictionary and thesaurus tools; something whose input requires reading teaches reading. They've dropped various tablets off in remote areas, and without teachers they've taught themselves to read and speak English...
Those are the big 4 subjects. None would "do the work for them"... just replace items already in use at a lower cost. The list could continue to other subjects easily as well. I'd even stretch to include Phys Ed, since apparently stacking cups is the new thing in gym... stacking cups. If stacking cups is physical education because of hand dexterity required, then a keyboarding class is gym as well... and Fruit Ninja should be too. (that phys ed part... it's a joke, based in reality tho).
And I tip 20%...