Thanks, Antartica. So I will try first [on my to-do list on top] to create pdf files in version 1.5 [status quo of Acrobat 6]. Then I will see.
Yes I have known ImageMagick, but it doesn't support djvu as native format, as you already said.
@ b_k: Exactly this will I do!
Other idea: Perhaps the iLiads pdf viewer can't handle tifs encoded in 1 bit CCITT Group 4 correctly.
This evening I will be wiser.