Put file contents as PDF comment (respecting UTF-8)

Question

I want to have file contents rendered as comment in a PDF file. I decided for pdfcomment, which works. pdfcomment requires newlines being typeset as \textCR\textLF. Which leas me to the following setting:

I would like to read the contents of a file, replace a newline by \textCR\textLF and have this passed to pdfcomment. As additional challenge, character sequences such as {, \_, .. need to be preserved.

Rough example:

demo.bib:

@article{demo,
  author = {Demo Frühling},
  comment = {Fr\"{u}hling}
}

After reading the file, following text should be passed to pdfcomment:

@article{demo,\textCR\textLF
  author = {Demo Frühling},\textCR\textLF
  comment = {Fr\"{u}hling}\textCR\textLF
}\textCR\textLF

Longer desired result:

\pdfcomment[icon=Help]{
@article{demo,\textCR\textLF
  author = {Demo Frühling},\textCR\textLF
  comment = {Fr\"{u}hling}\textCR\textLF
}\textCR\textLF}

Example with (non-working) code

\documentclass{article}
\usepackage{pdfcomment}
\newread\reader
\begin{document}
\begin{filecontents}{demo.bib}
@article{demo,
  author = {Demo Frühling},
  comment = {Fr"{u}hling}
}
\end{filecontents}
\pdfcomment[icon=Help]{
\makeatletter
\advance\endlinechar @M
\openin%
\reader=demo.bib%
\relax
\loop
    \read\reader to \x
    \unless\ifeof\reader
    \x \textCR\textLF
\repeat
\closein\reader
\advance\endlinechar -@M
\makeatother
}
\end{document}

That renders to following:

This is not the thing, I intended. The comment should have the full text of the file.

Solution Thoughts

• I played around with catchfile, but with no success. (Related question: \CatchFileDef vs ( \input or \@@input ))
• I think datatool with \DTLforeach could work somehow, but I don't how to read a non-CSV file with data tool
• readarray looks good with readrecordarray, but I don't know how to craft a for loop, especially the end condition is unclear to me. Related answer: https://tex.stackexchange.com/a/116901/9075

Answer 1

Actually easy - i am just not sure if one can easily include the linebreaks, but i am sure you are going to find out. Using expl3 because it's much more readable in there ;-)

\documentclass{article}
\usepackage{pdfcomment}
\begin{filecontents}{demo.bib}
    @article{demo,
        author = {demo}
    }
\end{filecontents}
\begin{document}
\ExplSyntaxOn
\file_get:nnN {demo.bib} {
    \char_set_catcode_other:N _ 
    \char_set_catcode_other:N $
    \char_set_catcode_other:N {
    \char_set_catcode_other:N}
} \l_tmpa_tl
\exp_args:NnV \use:n {\pdfcomment[icon=Help]}{\l_tmpa_tl}
\ExplSyntaxOff
\end{document}

And just in case you don't want to change all characters to other manually you could also iterate over a squence and read the file as a string:

\documentclass{article}
\usepackage{pdfcomment}
\begin{filecontents}{demo.bib}
    @article{demo,
        author = {demo}
    }
\end{filecontents}
\begin{document}
\ExplSyntaxOn
\ior_new:N \l_tmpa_ior
\ior_open:Nn \l_tmpa_ior {demo.bib}
\seq_clear:N \l_tmpa_seq
\ior_str_map_inline:Nn \l_tmpa_ior {
    \seq_put_right:Nn \l_tmpa_seq {#1}
}
\exp_args:Nnx \use:n {\pdfcomment[icon=Help]}{\seq_use:Nn \l_tmpa_seq {\textLF}}
\ExplSyntaxOff
\end{document}