[1] Re: Font MIME types (Chris Lilley 著, 版) <https://lists.w3.org/Archives/Public/www-style/2015Apr/0335.html>
TrueDoc Portable Font Resource was implemented in a browser (in Netscape 4) but is no longer relevant; with the move from closed-source Netscape to open-source Mozilla that format, which required payment of license fees to Bitstream, was dropped.
[2] RFC 3073 - Portable Font Resource (PFR) - application/font-tdpfr MIME Sub-type Registration ( 版) <https://tools.ietf.org/html/rfc3073>
[3] RFC 3073 - Portable Font Resource (PFR) - application/font-tdpfr MIME Sub-type Registration ( 版) <https://tools.ietf.org/html/rfc3073>
The PFR media type has been previously registered with IANA as
application/vnd.truedoc. In view of its subsequent widespread
adoption as a standard font format by multiple standards bodies who
have relationships with the Internet community, Bitstream has been
asked to re-register this media type within the IETF tree.
[4] TrueDoc - Bitstream ( 版) <http://web.archive.org/web/20040603123430/http://www.bitstream.com/categories/developer/truedoc/pfrspec.html>