The required format for -injdf absolute file paths is 'file:///...' (but not for other parameters). E.g.
.\JDFPrintProcessor.exe -injdf "file:///c:/Temp/PrintMyPDF.jdf" -outdir "C:\Temp\output"
Correct output is:
>>>> Submitting J O B 0 to JDF Player <<<<<
>>>> Job 0 was received on command line
>>>> Job 0 URL is file:///c:/Temp/PrintMyPDF.jdf
[TiffFile: PrintMyPDF001_p00.tif,1,0,Cyan,5100x6600]
[TiffFile: PrintMyPDF001_p01.tif,1,1,Magenta,5100x6600]
[TiffFile: PrintMyPDF001_p02.tif,1,2,Yellow,5100x6600]
[TiffFile: PrintMyPDF001_p03.tif,1,3,Black,5100x6600]
[JobTime Job 0: PrintMyPDF, 0.652 sec.]
<<<<< Job 0 processing completed: Successful >>>>>
Terminating JDF Print Processor
Hope this saves someone some time (including my future self)