Problem when printing with opacity in my document

Hi,

I got an issue when I'm trying to print a document with like 50% opacity in it (with watermark actually), which is really pissing me off. PDF files has been made with PDF architect.
In fact, when i'm trying to print them, watermarks become fully opaque. On the document opens in PDF architect, the preview is alright.And it's not an issue with the printer, it's the same thing when I'm trying to print via the microsoft XPS printer, or with several real printers.

Do you have any idea what could be wrong?

best regards,

Gaetan