Yes, you can, but you may want to be careful about how you do it.
Before anything has been signed, you and your employer are really two parties bargaining, so if there is something else that you were looking for (a salary increase, a change in your bonus, extra vacation) then the best time to negotiate these things might be before you sign anything at all. Remember though that if you’re bargaining with your employer, they may ultimately hold the bargaining power. If you start making requests that are totally out of line with their initial offer, they have the power to pull the job offer entirely before you’ve accepted.
There are pieces though that you will likely want to negotiate in any job offer, especially if you are looking at more senior or professional roles. We can advocate for you during this process, and help make sure that the offer is worthy of the talent and experience that you bring to the role.