Hello,
Thanks for reaching out and for your interest in CryptPad!
There is no way to disable copy/paste. Even if it was possible I should say that it's a very easy thing to overcome thanks to all the nice Optical Character Recognition (OCR) solutions out there now.
On Apple macOS & iOS, you can simply take a photography or a screenshot of what is shown on screen and then select the text from it and copy it.
Hope this helps!