(This is an issue I originally posted here: http://tex.stackexchange.com/questions/58760/lualatex-fontspec-cannot-compare-documents-with-acrobat and I cross-posted on the LuaTeX User Mailing list)

I use the option "compare documents" in Adobe Acrobat Pro a lot to highlight changes between revisions. What I just noticed is, if I compile a simple document such as the one below with LuaLaTeX + fontspec, Acrobat is unable to perform the comparison, giving a unspecific error message ("cannot compare document..."). Compiling the same document without fontspec allows the comparison, as does XeLaTeX + fontspec.

I tried with TeX Live 2012 and the current MikTeX, without success. Ulrike Fischer suggested \usepackage{luaotfload} \font\test=Arial \pagestyle{empty} and \test after \begin{document} instead of fontspec, but the error remains. Does anyone know what is going on and of a possible fix?

\documentclass{article}

\usepackage{fontspec}

\usepackage{lipsum}

\begin{document}

\lipsum

\end{document}

Best,

Jörg