This document refers to an incident where an SS man named Theuer was almost killed by accidentally inhaling some gas fumes from Zyklon B after an overnight fumigation. That some of the gas was caught in a few "pockets" is not unusual in areas treated by Zyklon. The incident was examined at length during the Auschwitz Trial by the former head of disinfestation and fumigation at Auschwitz, Artur Breitweiser. He was declared innocent of any crimes by the court.
It was published by Jean Claude Pressac in his Auschwitz: Operation and Technique of the Gas Chambers. At page 188, Pressac writes:
"This text, which previously appeared to be damning proof of the existence of homocidal gas chambers can no longer be accepted as such."
As Pressac noted, 42 copies of the document were made; therefore it was not at all secret. The document clearly is dealing with fumigations and delousing. Exterminationists stay clear of this document these days because it directly contradicts their claims of "twenty-minute gassings".