copy protected pdf files

[A. R. Vener]

I purchased  a set of instrucional CD's which contain  some
files in pdf format.

Unfortunately when I try to convert them with  pdf2txt, I get a message stating tthat the text 
cannot be copied.


Once upon a time I vaguely recall hearing that there is a single bit in the pdf file
that sets the copy protected  mode.
Can anyone tell me if this is so and what the offset and bitmask would be?

Thanks,
Rudy