Hello, I have the following markdown source, containing some latex macros and I would like to convert it both to html and pdf.

---
title: Hello
---

\DeclareMathOperator*{\E}{\mathbb E}

This is some math: $\E x$

I can convert it to html, using `pandoc hello.md --mathml -s -o out.html`, but conversion to pdf fails (complaining that \DeclareMathOperator can only be used in the preamble):

$ pandoc hello.md -f markdown-latex_macros -s -o out.pdf
Error producing PDF.
! LaTeX Error: Can be used only in preamble.

I can successfully convert the markdown to pdf, by moving the macros to a separate `macros.tex` file and including it with `-H`, however I would like to keep a single input markdown file, which should be converted to both html and pdf.

Having the macros in a separate file would be ideal, so I could avoid duplicating them in each source file.

I also tried to make a lua filter to dynamically include `macros.tex` when converting to html, but it does not seem to work.

mt, contents = pandoc.mediabag.fetch("etc/macros.tex", ".")
macros = pandoc.read(contents).blocks

function Pandoc(doc)
return pandoc.Pandoc(macros .. doc.blocks, doc.meta)
end

Could anyone give me any hints?

Thank you,

Germano