Edward,

The DocumentExporter object exposes the ExportPage method.  That method accepts the document (cast as a DocumentInfo ), the page number (1 based), and the stream or file path to export to.  From the SDK documentation;

public void ExportPage(
	IDocumentContents document,
	int pageNumber,
	string outputPath
)

The DocumentExporter.PageFormat property will allow you to select the DocumentPageFormat.Jpeg enumeration to export the document as a JPG.  In addition the DocumentExporter.CompressionQuality property will allow you to set the quality of the exported image.  The compression ranges from 0 (most compression, lowest image quality) to 100 (least compression, highest image quality).