The General Instruction to The Roman Missal. Also, it seems to me that Pope Paul decreeing that it would be the ordinary liturgy of the Latin rite is promulgation.
I have to side with Unregistered Guest on this issue. Paul 6's decree announcing the Novus Ordo is entitled, Missalae Romanum
, the same title as Pope Pius V's document. The General Instruction for the Novus Ordo does not actually promulgate the Novus Ordo, it merely explains how it is to be performed (and I use that word intentionally).
Paul 6's document also does not actually promulgate the Novus Ordo either. In fact, upon reading the document it actually makes two commands:
1. That the "words of the Lord be identical in each form of the canon" in this new missal; and,
2. That the effective date is the First day of Advent of the current year.
Frankly, Paul 6 doesn't even authorize anyone to say this new mass let alone require anyone to say this new mass.
The fact is that, in spite of these facts, just about everyone took the new mass as being obligatory and ruthlessly persecuted anyone who refused. There simply is no actual law, even in the Conciliar Church, that allows, authorizes, or requires anyone to use the Paul 6 Missal.