Yes, that was also hinted by ottdmk... But in either case it is a clear bug in kobo software...
EDITED:
I've opened ottdmk's pdf and Canon one in Adobe Reader XI and
both are password protected for certain areas. I upload two screenshots, they are in Spanish but I suppose you'll easily understand/translate them.
Nevertheless the key differences:
- Canon one requires Acrobat X or later, ottdmk's one just 7.0.
- Canon one uses 256bit AES encription. ottdmk's one uses only 128bit AES encription
If I get across some other conflictive pdf I'll check its protection properties.