[AUCTeX] pdfsizeopt does not work when called from Emacs, but works when called from cmd.exe

[AW]

Hi!

Strange Emacs and maybe AUCTeX issue.

Emacs-Version: GNU Emacs 25.1.1 (x86_64-w64-mingw32), AUCTeX: 11.91.0. We are 
on Windows 8.1.

I'm using pdfsizeopt to shrink the PDFs produced with AUCTeX. I installed 
various times pdfsizeopt according to the manual, see here:
https://github.com/pts/pdfsizeopt

pdfsizeopt works, but _only_ if called from cmd.exe. Output is this:

#+BEGIN_SRC 

R:\Bilder\...>pdfsizeopt.exe 170802-XXX.pdf 170802-XXX.pdf
info: This is pdfsizeopt ZIP rUNKNOWN size=114611.
info: prepending to PATH: C:\pdfsizeopt\pdfsizeopt_win32exec
info: loading PDF from: 170802-XXX.pdf
info: loaded PDF of 840447 bytes
info: found 83 obj offsets and 1 obj streams in xref stream
info: separated to 81 objs + xref + trailer
warning: cannot parse obj 19: pdfsizeopt.main.PdfIndirectLengthError: missing 
ob
j for indirect /Length 40 0 R at ofs=20930
... [many more messages]
info: found 6 Type1 fonts loaded
info: writing Type1CConverter (417100 font bytes) to: psotmp.3232.conv.tmp.ps
info: using Ghostscript "C:\pdfsizeopt\pdfsizeopt_win32exec\pdfsizeopt_gswin
\gsw
in32c.exe": GPL Ghostscript 9.02 (2011-03-30)
info: executing Type1CConverter with Ghostscript: "C:\pdfsizeopt
\pdfsizeopt_win3
2exec\pdfsizeopt_gswin\gswin32c.exe" -q -P- -dNOPAUSE -dBATCH -
sDEVICE=pdfwrite
-dPDFSETTINGS=/printer -dColorConversionStrategy=/LeaveColorUnchanged -
sOutputFi
le=psotmp.3232.conv.tmp.pdf -f psotmp.3232.conv.tmp.ps
Type1CConverter: using interpreter GPL Ghostscript 902 20110330
Type1CConverter: converting font /TBQTVH+LinBiolinum to /Obj0000000070
Type1CConverter: converting font /DAOZLD+LinBiolinumI to /Obj0000000072
Type1CConverter: converting font /SEISLV+LinLibertineB to /Obj0000000074
Type1CConverter: converting font /MNLYJI+LinLibertine to /Obj0000000076
Type1CConverter: converting font /WBBRJQ+LinLibertineI to /Obj0000000078
Type1CConverter: converting font /MKHCTZ+LMMathSymbols8-Regular to /
Obj000000008
0
Type1CConverter: all OK
info: loading PDF from: psotmp.3232.conv.tmp.pdf
info: loaded PDF of 28886 bytes
info: separated to 28 objs + xref + trailer
info: found 6 fonts in GS output
info: optimized total Type1 font size 417168 to Type1C font size 20657 (5%)
info: optimized Type1 font XObject 70,69: new size=7149 (9%)
info: optimized Type1 font XObject 72,71: new size=3093 (5%)
info: optimized Type1 font XObject 74,73: new size=2665 (3%)
info: optimized Type1 font XObject 76,75: new size=7473 (7%)
info: optimized Type1 font XObject 78,77: new size=1646 (2%)
info: optimized Type1 font XObject 80,79: new size=658 (25%)
info: found 6 Type1C fonts loaded
info: writing Type1CParser (20533 font bytes) to: psotmp.
3232.conv.parse.tmp.ps
info: executing Type1CParser with Ghostscript: "C:\pdfsizeopt
\pdfsizeopt_win32ex
ec\pdfsizeopt_gswin\gswin32c.exe" -q -P- -dNOPAUSE -dBATCH -sDEVICE=nullpage -
sD
ataFile=psotmp.3232.conv.parsedata.tmp.ps -f psotmp.3232.conv.parse.tmp.ps
Type1CParser: using interpreter GPL Ghostscript 902 20110330
Type1CParser: all OK
info: parsed 6 Type1C fonts
info: writing Type1CGenerator (58243 bytes in 6 fonts) to: psotmp.
3232.conv.gen.
tmp.ps
info: executing Type1CGenerator with Ghostscript: "C:\pdfsizeopt
\pdfsizeopt_win3
2exec\pdfsizeopt_gswin\gswin32c.exe" -q -P- -dNOPAUSE -dBATCH -
sDEVICE=pdfwrite
-dPDFSETTINGS=/printer -dColorConversionStrategy=/LeaveColorUnchanged -
sOutputFi
le=psotmp.3232.conv.gen.tmp.pdf -f psotmp.3232.conv.gen.tmp.ps
Type1CGenerator: using interpreter GPL Ghostscript 902 20110330
Type1CGenerator: all OK
info: loading PDF from: psotmp.3232.conv.gen.tmp.pdf
info: loaded PDF of 28079 bytes
info: separated to 34 objs + xref + trailer
info: found 6 fonts loaded
info: optimized Type1C fonts to form 21874 bytes to 21862 bytes (100%)
info: eliminated 23 unused objs in 23 classes
warning: obj 19 missing, referenced by objs [16]...
warning: obj 20 missing, referenced by objs [16]...
...[many more messages]
info: compressed 2 streams, kept 2 of them uncompressed
info: saving PDF with 37 objs to: 170802-XXX.pdf
info: generated object stream of 2287 bytes in 27 objects (17%)
info: generated 38966 bytes (5%)

R:\Bilder\...

#+END_SRC

But it does not work, if I call it from Emacs!

Command:
#+BEGIN_SRC 
pdfsizeopt.exe "170802-XXX".pdf "170802-XXX".pdf
#+END_SRC

Output:
#+BEGIN_SRC 
Running `pdfsizeopt' on `170802-XXX' with ``pdfsizeopt.exe "170802-XXX".pdf 
"170802-XXX".pdf''
info: This is pdfsizeopt ZIP rUNKNOWN size=114611.
info: prepending to PATH: C:\pdfsizeopt\pdfsizeopt_win32exec
info: loading PDF from: 170802-XXX.pdf
info: loaded PDF of 38966 bytes
info: found 39 obj offsets and 1 obj streams in xref stream
info: separated to 37 objs + xref + trailer
info: found 0 Type1 fonts loaded
info: found 6 Type1C fonts loaded
info: writing Type1CParser (20521 font bytes) to: psotmp.
5260.conv.parse.tmp.ps
Traceback (most recent call last):
  File "C:\pdfsizeopt\pdfsizeopt_win32exec\python26.zip\runpy.py", line 122, 
in _run_module_as_main
  File "C:\pdfsizeopt\pdfsizeopt_win32exec\python26.zip\runpy.py", line 34, in 
_run_code
  File "C:\pdfsizeopt\pdfsizeopt.single\__main__.py", line 1, in <module>
  File "C:\pdfsizeopt\pdfsizeopt.single\mainrun.py", line 10, in <module>
  File "C:\pdfsizeopt\pdfsizeopt.single\pdfsizeopt\main.py", line 8919, in 
main
  File "C:\pdfsizeopt\pdfsizeopt.single\pdfsizeopt\main.py", line 6438, in 
OptimizeType1CFonts
  File "C:\pdfsizeopt\pdfsizeopt.single\pdfsizeopt\main.py", line 6084, in 
_ProcessType1CFonts
  File "C:\pdfsizeopt\pdfsizeopt.single\pdfsizeopt\main.py", line 5571, in 
ParseType1CFonts
  File "C:\pdfsizeopt\pdfsizeopt.single\pdfsizeopt\main.py", line 140, in 
GetGsCommand
AssertionError: Could not find a working Ghostscript.

TeX Output exited abnormally with code 1 at Wed Aug  2 12:35:31

#+END_SRC

So why on Earth does pdfsizeopt within Emacs not find "a working ghostscript",
while called from cmd.exe inside any folder of the network here runs smoothly?

Please note that I asked this question at stackexchange whithout answer and on 
the website of pdfsizeopt. So if you can rule out that it is an AUCTeX issue, 
my last resort would be the Emacs-Developer mailing list...

Thanks for any help!

Kind Regards,

Alexander