Getting fontspec Fonts with pdfLaTeX

Question

I have to make a document, which was originally written in LuaLaTeX, compatible for both pdfLaTeX and LuaLaTeX. Everything works except that the fonts differ. How can I force pdfLaTeX/fontenc to use the same fonts as fontspec?

Minimal example (omitted ifluatex to avoid clutter):

\documentclass[fontsize=11pt]{scrreprt}
% \usepackage{fontspec}
\usepackage{lmodern}
\usepackage[T1]{fontenc}
\usepackage[utf8]{inputenc}

\begin{document}
    \chapter{Chapter}
    \section{Section}
    Text with some formulas: $a=1$.
\end{document}

By using lmodern, the fonts of the text seem to almost coincide, but the math fonts differ:

# pdffonts output for pdflatex with lmodern, fontenc and inputenc:
name                                 type              encoding         emb sub uni object ID
------------------------------------ ----------------- ---------------- --- --- --- ---------
ZGMFNK+LMSans10-Bold                 Type 1            Custom           yes yes no       4  0
YIMXCY+LMRoman10-Regular             Type 1            Custom           yes yes no       5  0
GXEVRM+LMMathItalic10-Regular        Type 1            Custom           yes yes no       6  0
YIMXCY+LMRoman10-Regular             Type 1            Custom           yes yes no       7  0

# pdffonts output for lualatex with fontspec:
name                                 type              encoding         emb sub uni object ID
------------------------------------ ----------------- ---------------- --- --- --- ---------
SSPBGH+LMSans10-Bold                 CID Type 0C       Identity-H       yes yes yes      4  0
XXBUAG+LMRoman10-Regular             CID Type 0C       Identity-H       yes yes yes      5  0
EDWHGC+CMMI10                        Type 1            Builtin          yes yes no       6  0
HVZLMP+CMR10                         Type 1            Builtin          yes yes no       7  0

So, the type and encoding differs, and the math fonts.

Answer 1

It is not possible to get the same font encodings for LuaTeX and pdfTeX, for the simple reason that LuaTeX with fontspec uses OpenType fonts, whereas pdfTeX uses Type 1 fonts. It is possible to get the same math fonts, though, by passing the option nomath to lmodern.

If you are using the 2018 version of LaTeX, you can remove \usepackage[utf8]{inputenc} because UTF-8 is now the standard encoding.

\documentclass[fontsize=11pt]{scrreprt}
\ifdefined\directlua
  \usepackage{fontspec}
\else
  \usepackage[T1]{fontenc}
  \usepackage[nomath]{lmodern}
\fi

\begin{document}
    \chapter{Chapter}
    \section{Section}
    Text with some formulas: $a=1$.
\end{document}

Run through pdflatex I get this

$ pdflatex test.tex
$ pdffonts test.pdf
name                                 type              encoding         emb sub uni object ID
------------------------------------ ----------------- ---------------- --- --- --- ---------
ZGMFNK+LMSans10-Bold                 Type 1            Custom           yes yes no       4  0
KOIJYY+LMRoman10-Regular             Type 1            Custom           yes yes no       5  0
EDWHGC+CMMI10                        Type 1            Builtin          yes yes no       6  0
HVZLMP+CMR10                         Type 1            Builtin          yes yes no       7  0

Run through lualatex I get this

$ lualatex test.tex
$ pdffonts test.pdf
name                                 type              encoding         emb sub uni object ID
------------------------------------ ----------------- ---------------- --- --- --- ---------
SSPBGH+LMSans10-Bold                 CID Type 0C       Identity-H       yes yes yes      4  0
HXVMKT+LMRoman10-Regular             CID Type 0C       Identity-H       yes yes yes      5  0
EDWHGC+CMMI10                        Type 1            Builtin          yes yes no       6  0
HVZLMP+CMR10                         Type 1            Builtin          yes yes no       7  0