[luatex] UTF-16 with pdfe.getstring()

[Andreas Matthias]

I'm having a hard time with pdfe.getstring(). What am I supposed to do if it
returns an UTF-16 encoded string? How to convert it to UTF-8?

Here is what I'm actually trying to do: I'm reading the /Contents of a
Text-Annotation
with pdfe.getstring(). The returned string happens to be UTF-16
encoded. Now I want to
use this string to create a pdf_annot whatsit. Of course this doesn't work:

This is LuaTeX, Version 1.13.0 (TeX Live 2021/dev)
 restricted system commands enabled.
(./test.tex
! String contains an invalid utf-8 sequence.
l.17 }

I've attached an example to replicate this issue.

Andreas
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