Best Method of Distributing a Journal/Magazine PDF on CD

Hi,

I'm working on a project for a non-profit that publishes a 125-page journal twice a year. They want to sell their whole collection of journals on CD. They currently have about 50 issues which I’m in the process of scanning and running OCR on.
I am trying to get advice as to the best method of putting these on CD and selling them.

The requirements in short are:
-Search capabilities throughout all 50 issues preferably with the ability to search only specific journals (years 1990 to 1995 for example)- This needs to be as simple for the user as possible

-Some sort of protection so one buyer can't simply send the PDF(s) around to all his/her friends. But at the same time we don't want it to be a difficult process in order to read them.

Is it feasible to put aprox 6,500 pages into one nicely indexed PDF to make the search simple or will that freeze people's systems up?

Any help would be greatly appreciated.

Thanks,
Daniel