I tried installing the CIS 2.1.2 and 2.1.3 firmware versions for my 902, and the PDF files viewed with AdobeViewer looked the same as with my North America 2.1.3 firmware version. I even tried copying over the AdobeViewer applications from the CIS 2.1.2 and 2.1.3 912 firmware versions, but they also looked the same. I guess the German firmware versions you (@crt) had were particularly bad for PDF files, since everything else looks to be the same.
I did notice that 2.1.2 was slower than 2.1.3 in the menus. Maybe it would be worth upgrading to 2.1.3 for you, since the PDF viewing looks the same in both.