In article , Carlos E.R.
wrote:

There is a published PDF standard, which they no longer own.

i said that.

But they
can add, and do add, additional features that only them support properly
(because they don't publish).

as can others, however, content creators are not required to use them,
and it would be foolish to do so. it's rare that a pdf on a web site is
anything fancy.

On the contrary. Most government forms and complex forms I have seen use
them.

forms are not adobe proprietary.

i've never seen a single pdf posted for public consumption that uses
adobe extensions in more than 20 years.

where it's used is when everyone is using the same software, normally
*within* graphic arts and publishing companies.