If you want do spotting at Paris CDG, you must have a photo permit delivered by authorities.
Personnaly, I've aksed mine more than 1 year ago and I'm still waiting .

You can try some photos but police or security services can check if you have this famous permit.

Many more spotters are waiting this permit since a long long time ago. You can try ask permit by sending email in french (recommended, use google translate) to the following address:
spotters [at] interieur.gouv.fr with your ID/Passport copy, home address and some text to explain.