You have no obligation to sign the NDA at this point. If you want to keep a positive relationship with this company and it has nothing to do with your new job

You have no obligation to sign the NDA at this point. If you want to keep a positive relationship with this company and it has nothing to do with your new job then you might consider signing it. I would do so only after having a lawyer take a quick look, though. I would also make sure it has an expiration, like 1 year.