What's the difference between promulgate and enact?
The differences are subtle in practice today as a result of technologies like the Internet.
Enact means (according to Black's Law Dictionary, 5th edition (1979), hard copy):
To establish by law; to perform or effect; to decree. The common introductory formula in making statutory laws is, "Be it enacted."
Promulgate means (according to the same source):
To publish; to announce officially; to make public as important or obligatory. The formal act of announcing a statute or rule of court.
In the context of the U.S. legislative process, a law is enacted at the moment when it is signed by the President or Governor after being duly passed by the legislative branch (or when it is adopted by the legislative branch in a veto override).
It is promulgated when the public act is published either in physical book form, or electronically, for example, in an online official government website containing the laws that were enacted.
These days the time gap between enacting a law and promulgating it is a matter of minutes or hours. Historically, the gap would have been a matter of days or weeks.
For example, in Colorado, the legislative session ends in the first few days of the month of May, with all laws passed during the session signed or vetoed by mid-May, but (subject to certain exceptions) laws passed in that session are generally effective on July 1 of the same year. This reflected the assumption of the people who drafted that part of the state constitution that it could typically take up to about four to six weeks to promulgate the laws enacted in the legislative session.