Cant touch this...read/write restriction

Heres the thing see. If I want to show someone some work i have done. I can send it to them then give them a password to open the file and so they can see it. However, when I give them a disk or use one of my own - they can still copy the document to thier own machine. If it open you can just do save as and asve it as another file with no password. So you can disable saving. But then you can jsut copy the source file and you would still know the password. How can I write files to CD or floppy and disable the abilty to copy the file from the disk to anywhere else. That way I can lend someone a disk with my work on let them look - disable saving so they cannot do a save as and also deny them the right to copy the file to thier own machine or disk.

Is it worth looking into encryption for this type of thing or am i barking up the wrong tree alltogether.
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Acid