Date from mm/dd/yyyyy to Date Custom dddd, mmm dd, yyyy

++Adding to the topic,

This is not a bug as pointed out by @try67 and also @JR Boulay is absolutely correct about employing the correct concept of ISO date standards.

The issue that you've observed happens with both the month and the day values depending on how they are interpolated in the date notation.

What is truly missing in this conversation is a small observation but with a more detailed, long and boring (yet important) clarification.

The date notation standards have been unique throughout history since the Old World versus the New World colonization. And the way that the date/time should be used with written formal papers, or expressed grammatically when publishing citations, to include military or International date/time standards accross the globe, have a reason and its purpose.

If you dig some more about why the US is the only country in the world that employs a date notation in which the month comes before the day , and more specifically with short date expressions (such as mm/dd/yy) that are accepted only by North Americans, you will see clearly why the Acrobat JavaScript core interpreter throw an alert to the user simply to point out an error with the date notation that is employed with that document.

For example, as opposite to the US , Europeans (and mostly every other country in the world, with the exception of some Asian nations that use ISO standard yyyy-mm-dd), are OK with dates that are expressed with the day before the month as the official date notation standard.

And if we take the same premise and apply it to how to use  short expression dates (such as "03/18/19") in a paper or a formal document, it would make it really hard for different users accross the world to understand what is the day, what is the month, and even the century that the publication (or PDF document in this case) is citing.

In other words, even though in the US it may be accepted (or considered OK) to cite a date informally, like for example "Fri, March 03, 2023" or "Friday, Mar 3, 2023", this doesn't necessarily means that it is also correct to turn an US short date into a long date notation format (like the one you are trying to force with your PDF): "Fri, 03/18/23"... specifically where the day of the week comes before the month, but the month is notated before the calendar day and expect every person in the world could (or should, or would) understand what exaclty is the date that you are trying to express.

In which case, if you use that format the short date notation is no longer short, but a long date notation format.

So, if you are going to do that, then (from the propper grammar standards in writing and formal date expressions standards) you may not abbreviate the day and the month; it has to be explicitely worded out like "Friday, March 04, 2023".

You will notice that if you express the date notation like "ddd, mmm/dd/yy" in Acrobat it will work. Nevertheless,  it is grammatically incorrect and much less the proper date notation standard.

If we break down further your desired current date notation, Note that you are citing an abbreviated day of the week "Fri" and immediately jump to the month number "mm/" notation, then jump back to the calendar day notation "dd/" and lastly the abbreviated year notation "yy" (dashes, periods, or slashes are irrelevant in this context).

With all that said, instead of using "ddd, mm/dd/yy" (where the month comes before the calendar day), you must interpolate the calendar day notation before the month number notation like shown in this long date notation: "ddd, dd/mm/yy" in order to make it acceptable as an informal date expression.