I use Gembox.Pdf (1.5) to merge different PDF streams to one PDF stream. I do that exactly as it is shown in the example.
The PDF stream is generated correctly (as far as I can say, because I can open the generated PDF in a PDF reader), but if I generate a XPS from the document, I get:
System.IO.FileFormatException: ‘Invalid file format.’
If I print the documents (the generated XPS) separately, everything is fine. So I think there must be something wrong with the merged document.
I could send you a example project with some PDFs to merge if you want.