I used to work for a defense contractor, in the mid-1980s.

Once a week, this big-ass tandem truck would park outside the entrance, and the janitors would carry out boxes of papers, under armed guard.

The truck had a huge shredder (crosscut), and also a big kiln.

Once the paper was shredded, it was burned, and the ashes were shredded, just to be sure.

Then, the truck would take the ashes away; never to be seen again.