PDF Default fonts: Symbol vs. unicode

[mathog]

PDF requires that all viewers support a set of default Postscript fonts.
These fonts are not unicode, or at least, were not originally.
One of these is Symbol.
Symbol was not, and still is not, a unicode font.
Another of these is Times New Roman, which is usually now a unicode
font, at least on Macs and Windows machines.

Most web and a lot of other modern applications only do Unicode, or only
do unicode well. For instance, from recent unpleasant experience, Pango
(text layout library) does what it should with Symbol font characters in
the ASCII range, and does all sorts of crazy things with characters >=
0x80. For instance, the "greater than or equal to" character shows up
as a superscript 3.

The unicode way is to encode Symbol fonts using their unicode
equivalents, most of which exist.

Which brings us at last to the question - if Symbol characters are all
converted to unicode and into the font Times New Roman, are PDF viewers
required to support the complete font, the full unicode, or only the
first 256 characters of the font? If full unicode support is not
required how would one tell ghostscript to embed partial fonts as needed
for those unicode characters that are outside of the default set?

Thanks,

David Mathog