This is the reverse idea of [xenzag]s Gobbledback Paper from several years ago (linked).
Paper printed by the ream with a nearly invisible, microscopic, non-repeating fractal pattern. Could be done with dyes that only show up under UV, or incorporated in watermarks or the weave of the paper fibers.
It would have to be nearly impossible to detect unless you knew exactly what to look for.
Someone hoping to exploit this would have to set up large scale manufacturing and marketing, so they could become a competitive mass supplier of paper - to many customers as well as their eventual unsuspecting targets.
When needed at some future date - e.g., after somehow acquiring a load of torn or shredded documents - re-assembly would be much easier. Software does exist to re-image shredded documents, but embedded markings could speed that up. In a Spy vs Spy way, this might be used by spies trying to steal secrets, or by NARA trying to recover maliciously destroyed paperwork*.
* Not that any insiders would EVER do that.