I’d say don’t bother trying to parse it alone. Have a meeting where the person that created it presents it, and drill into anything weird.

If you can back them into a corner and force them to admit they don’t even understand something they supposedly wrote, use that as an opportunity to remind people it’s not acceptable to generate design documents that you don’t understand and then push them off onto other people.

Yeah, this. If it's slop, reject it, and tell them why.