Wayne,
I don't know a lot about workflow, but I just downloaded an XLSX file via the Platform SDK service and it came down in its native format, not PDF.
What export are you using? That's the part of workflow I am unsure of...? If it is a call to a web service that uses DocuWare's own Platform Service, then it should download as the actual file, not a PDF conversion.
Thanks,
Joe Kaufman