I've resolved my problem, so in case anyone else is running into this issue, I'll post the solution here.

The SubmitResultFile value is supposed to contain the job file resulting from from the completed planet process. My problem was that I was ending my process with the Image connector, which sets the job file as a postscript file. I changed that module to the Create PDF action which sets the job file as the resultant PDF.
My new process is 'Input SOAP' - 'Create PDF' - 'Delete'