Bug#962668: same error

[Michael Meier]

I've got exactly the same error (the one with the surrogates not 
allowed) with way too many PDFs. Already since months, always using the 
newest calibre version in testing.
Now I've just installed the official version as described in
https://calibre-ebook.com/download_linux
and that version does the conversion without any problems. So the 
problem must be in the debian package.