when i print pdf-files using print button (Print {Os!}) from Opus and foxitreader (pdf filetype-print:"C:\Work\PROGS\FOXITR~2\FOXITR~1.EXE"/p "%1" ) i can't print on ISO A0!!! All files goes on ISO A1! (format-1=result) what's this?
I doubt that Opus is changing which paper size that Foxit uses.
Try running a similar command from command prompt to confirm it.
Assuming this is to do with Foxit and not Opus:
same result 