Wouldn’t fire be easier and more effective
No, not really. Something like a phonebook burns more akin to a log than does paper but it doesn’t like to stay lit and things like thick fanfold printer output tends to absorb moisture from the environment, like a carribean island, so now it burns like a soggy green log. Since it doesnt stay lit someone has to keep stirring the pile and even then chunks tend to get lost in the ash.
Individual sheets of course burn well but when you throw it in a big pile and light it in the hopes of speeding the process up you find that air cant get between the sheets so it doesnt light or want to stay lit even with gasoline or diesel.
Either way you wind up with a big pile of evidence exposed somewhere.
To burn it you would need to take the time to crumple each sheet and make a giant pile or make big fat shreds that hold themselves apart like a pile of spaghetti and burn it in batches or it will compress in on itself again recreating the no air problem.
If your going to have to get equipment to do it quickly and you need to make sure none can reassemble it then you need either a shredder and an incinerator or better, as Greybeard mentioned above, a pulverizer.
A shredder alone is just a way to distribute secrets more slowly.
Sorry, I meant Greyfriar in 39.