As seen on the screenshot given in the URL, watermarks are not really rendered correctly. A bugreport in our (archlinux) bugtracker is over here: http://bugs.archlinux.org/index.php?do=details&id=3150 The PDF is located over here: http://consumer.usa.canon.com/ir/controller?act=DownloadDetailAct&fcategoryid=322&modelid=10149 (go to product/software manuals, download the english user manual to see the result). I think this bug is inherited from xpdf 3.0, since gpdf, which contains a fork of xpdf, also has this bug. xpdf 3.0.1 doesn't have the bug. The text in the PDF becomes visible when you select it in evince, so the text is rendered actually.
This sounds related to http://bugzilla.ubuntu.com/show_bug.cgi?id=17099, where the background of http://bugzilla.ubuntu.com/attachment.cgi?id=4427 is only rendered in xpdf (3.01), and not in evince (0.4.0) with poppler (0.4.2)
*** This bug has been marked as a duplicate of 3098 ***
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