PDFCreator creates the files using a special printer driver. To be able to print, you do not neccessarily need a file. In that case, there is no filename. Some applications (i.e. IrfanView) pass the filename to the printer driver. It can then be used with the <REDMON_FILENAME> Token. If your application does not provide this, it can be only captured by controlling the whole print process, i.e. using a script like Convert2PDF.vbs.