I'm lost at how you are getting pdf files into Gensolve, it doesn't show file types when uploading from a scanner, at least not on their official site support
The only time it deals in pdf it seems is when you save/export the file/report from Gensolve, which is long after the Xerox is done its job
And then they state this, but it doens't apply to single page, it applies to everything
The software should be the one deciding what format, not the TWAIN driver. It would not make sense for the driver to decide since it would not know what format the requesting app can read. It wouldn't be helpful to have TWAIN set to pdf when the application supports .pdf or .doc for instance.
Many programs will decide a single page doc that doesn't have OCR should be .jpg or .tiff.
You completely left out what 3rd party software as well as what printer.
I hae a workcentre scanner that uses TWAIN functionality to scan into a 3rd party piece of software. One of my scan profiles (ADF Single Page) scans in as jpg and not in as PDF, I cannot find where to edit these any of these settings.