Thanks for your response.
Because of using it in a batch-file I could temporary change the path-variable without a problem and after that it runs smoothly.
Is pandoc 2 searching for ( / needing) supporting-files from miktex / pdflatex? (and version 1.x doesn't do that?)
But that workaround is good enough for me.
Thanks for your quick help.

Am Mittwoch, 3. Januar 2018 19:42:23 UTC+1 schrieb John MacFarlane:

Generally this would happen if the program is not found
when pandoc tries to run the process. I'm not sure why that
would be.

Try just using --pdf-engine=pdflatex and putting the
relevant directory in your path (perhaps temporarily).

+++ 'K' via pandoc-discuss [Jan 03 18 04:03 ]:
>   Hi,
>   I'm using portable Versions of pandoc and miktex on a Windows System.
>   With pandoc 1.19.2.1 converting a markdown-File to PDF runs fine - the
>   used commandline looks like this:
>   D:\pandoc\pandoc_1.19.2.1\pandoc.exe -o docs\file.pdf
>   --latex-engine=D:\LaTeX\MiKTeX_2.9\miktex\bin\pdflatex.exe --toc
>   docs\file.md
>   After upgrading pandoc to 2.0.6 I have to change the parameter
>   --latex-engine to --pdf-engine. The new commandline that would be used
>   was this:
>   D:\pandoc\pandoc_2.0.6\pandoc.exe -o docs\file.pdf
>   --pdf-engine=D:\LaTeX\MiKTeX_2.9\miktex\bin\pdflatex.exe --toc
>   docs\file.md
>   Following is the response I get:
>   pdf-engine D:\LaTeX\MiKTeX_2.9\miktex\bin\pdflatex.exe not known
>   I have updated Miktex, but the result is the same. With 1.19.2.1 the
>   PDF will be created.
>   Thanks for any helpfull advice.
>   Greetings
>   Karsten
>