Force the spool file to be in raw format.
[read/write property] printRawSpoolFile([out, retval] VARIANT_BOOL *raw) printRawSpoolFile([in] VARIANT_BOOL raw)
If this property is set to true, XpdfViewer forces spool files to be in raw format. If set to false, the driver's default spool file format - which may be raw, EMF, or something else, depending on the driver - will be used.

The default value is true. Changing this to false is usually a bad idea, unless your application specifically requires it.

viewer.printRawSpoolFile = True