Unable to abort PDF input during preprocessing.
When a PDF file is going through the input phase (PDF2VDD), it first does a preprocessing step whereby it checks for any transparent objects which may need to be flattened. If during this step, which can take quite a while, the client decides to kill the job, right-clicking and selecting either "End" or Abort" doesn't take effect until the entire preprocessing is completed.
The PDF2VDD process is intended to run uninterrupted. If you abort the job during the pre-process phase, you may either Stop the PDF-IN input client within the GUI, or end the PDF2VDD.exe process in Task Manager.
UPDATED: March 22, 2017