\pdfcompresslevel=0
\pdfobjcompresslevel=0
\providecommand{\pdfxopt}{a-1b,mathxmp}
% XMP Metadata first
\begin{filecontents*}{\jobname.xmpdata}
\Title{Unicode: U₄(ℤ[1/√2, i]). — 
       ASCII: !"'()*+,-./:;<=>?@[]`|#$&~^_.
       Four escaped symbols: \% \backslash\ \{ \}.
}
\Author{Gödel\sep Escher\sep 
%ÅąŅƅǅȅɅ
ǅ
		Bach\sep 
        U₄(ℤ[1/√2, i]), !"'()*+,-./:;<=>?@[]`|#$&~^_, \% \backslash\ \{ \}}
\Subject{This is the abstract. It's about ℤ[1/√2, i] and other rings.  \mathbf{A\,+\,B \;=\; C*D/\alpha_{i}^{34}\beta}}
\Keywords{the group U₄\sep and other stuff\sep Some
       symbols: & # < > \copyright\ 2014\sp{20125621} }
\Copyright{Copyright \copyright\ 2014 \textLF The artist <currently> known as Ƭ̵̬}
\CopyrightURL{http://www.mathstat.dal.ca/~selinger/copyright.html}
\Creator{pdfTeX + pdfx.sty with \pdfxopt\space option}
\Journaltitle{abc \textLF \S \ddag \dots ÀÁÂÃÄ
%ÅąŅƅǅȅɅ  % A0 = 10100000
ÆÇÈÉÊËÌÍÎÏÐÑÒÓÔÕÖ×ØÙÛÜÝß 
%Ņ
%àĠŠƠǠȠ †  % 85 = 10001010
%⅀⅁⅒⅕⅘
% ⠱ ⠲ ⠵ ⠷
áâãäåæçèéêëìíîïðñòóôõö÷øùúûüýþÿ\P }
% \dag \ddag \dots \S \P }
% \textLF \(\mathbf{A}+\mathcal{B} = \mathfrak{C}*\mathsf{D}/\vec{\mathsfbf{E}}\widetilde{ab}\)}
\end{filecontents*}
%
\documentclass{article}
%\usepackage[a-1b,e-1,vt-1]{pdfx-16}
%\usepackage[utf8]{inputenc}
%\usepackage[OT1,T1]{fontenc}
\usepackage{amssymb}
\usepackage{sansmath}
\usepackage[\pdfxopt]{pdfx}
%\usepackage[LY1]{fontenc}
\usepackage[OT1,T1]{fontenc}

%\listfiles
\tracingstats=2
\begin{document}
\noindent
In this example, only the metadata matters; 
apart from checking accents: {\`a \'e \"u}
and whether other characters still work consistently:

\dag \ddag \dots \S \P \$ 
$\bullet\dots \dag\ddag $

{\makeatletter
%
%\def\this{119808} %{1D400}
%\HyPsd@ConvertToUnicode\this %\tracingall
%\show\this
%\pdfstringdef\this{\ensuremath{\mathbf{A}}}
%\show\this
}

\end{document}


Memory usage before: 692&171340; after: 203&171195; still untouched: 4812814

mathxmp
Memory usage before: 692&183143; after: 203&182998; still untouched: 4800985

allxmp
Memory usage before: 692&189509; after: 203&189364; still untouched: 4794613
