Paris museum pass

Yes, just get it when you arrive in Paris. Visitor Center at Gare du Nord

Don't stress. You can also buy them at the TI's around the city and in most of the sights included in the pass. I think someone even said you can buy it on the London side of the Eurostar (assuming that's where you're starting).

Thanks for your help. I will wait until I am Paris .
Joni

You could also wait till you get to the first museum or sight covered by the pass, you can buy it then (instead of a ticket) and activate it immediately. This is easier if your first sight isn't the Louvre or Orsay or Versailles but someplace smaller. If you do buy it before using it, be sure not to activate it until the first time you actually use it, since that's when the meter starts running, so to speak.