[OS X TeX] [includepdf, PDFpen] imprints don't work

[RA Friedrich Vosberg]

Morning.

I want to include a PDF file into another file by \includepdf{}. The  
PDF file to be included is imprinted by PDFpen with the word COPY.  
This imprint is displayed in PDFpen.app and in Preview.app as well.  
When I open only this PDF file in TeXShop the imprint is displayed too.

But when I typeset a TEX file that includes the respective PDF file  
the imprint in the included PDF file won't be shown. Why that?

What's wrong?

Kind regards, Friedrich