If my company is bought out, can the new company take away the PTO that I've already earned?

This is personal time or paid time off you have already earned. In most if not all state labor laws and federal laws, you cannot have earned time off deducted without actual use of that time. If you have earned that time and you have that time banked, you cannot have it taken away, even if there is new ownership or a merger. If any attempts are made to deduct from your time earned, you need to bring this up in writing and verbally to your personnel department or human resources and then you may need to bring it up to the state labor department if the internal mechanisms that should be in place to protect employees are lost.