Preflight droplet returns too early

Question

I want to convert a color PDF into grayscale. So I created a new preflight profile where nothing happens except color fixup:
Advanced > Print Production > Preflight
PDF Fixups > Convert to Grayscale
I saved the profile and created a Droplet named grey.exe.
When I call grey.exe smallSize_1MB.pdf everything  is fine. But when I have to convert a PDF having big filesize like grey.exe bigSize_160MB.pdf the Droplet .exe process returns before the preflight is done.
Problems: A script (e.g. a batch file) continues without waiting for the Droplet to finish. So the script cannot make use the Droplet's result, e.g. a preflight report or the converted PDF file.
Why does the Droplet's .exe process return too early? Everybody can test this with the help of the attached Droplet and the following batch scripts:
smallSize.bat (use something small, e.g. 1 MB or smaller):
copy /Y smallSize.pdf tmp.pdf
grey.exe tmp.pdf
echo "return"
pause
bigSize.bat (use something really big, e.g. 160 MB or bigger):
copy /Y bigSize.pdf tmp.pdf
grey.exe tmp.pdf
echo "return"
pause
Ideas, anyone?
Message was edited by: Droptix  I am using Adobe Acrobat 8.0 Professional.
Message was edited by: Droptix  As an alternative I can imagine to re-produce the Droplet's function by Interapplication communication (IAC) through OLE, see http://www.adobe.com/devnet/acrobat/interapplication.html -> if anyone can tell me how to do a grayscale conversion via IAC/OLE... would be great! I know the IAC/OLE basics, can open, save and edit PDFs but don't know how to convert. It would also be possible to use: Advanced/Print Production/Convert Colors > set all Document Colors to convert > set Blending profile for instance to Gray Gamma 1.8 > set conversion options to don't embed profile.

Answer 1

This is not a good way to do it. But this is the way I do it now...
It seems to work but there is no guarantee that it will work in the future, or even on all machines.
private static int WaitForAcrobatReady() {
  // Get the current Acrobat instance.
  var app = new Acrobat.AcroApp();
  // While a preflight (droplet) is running, app.GetNumAVDocs() will
  // not return ANYTHING, it will just hang.
  return app.GetNumAVDocs();
To sum up the efforts of the last weeks: Acrobat doesn't seem to be made for inclusion in other automation jobs. This is just another thing that doesn't work.
(I had to use the C# library PDFSharp to do other things that Acrobat can do really well only that it's not possible to set those properties, or start that kind of actions, from "outside".)