You can not be automatically evicted or given a rent increase or lose any of your previous rights. Beware, though, many landlords try to use the sale or foreclosure of a building to intimidate tenants. In a nutshell, nothing changes legally when a new landlord takes over. You do not have to fill out or sign this agreement it is for the landlord's convenience. For example, if you had an oral agreement to use the backyard and you fail to include this in your estoppel, you may lose that right.
Many new landlords try to force tenants to sign a new rental agreement.
Only if your landlord offers you the exact same agreement which you now have could you be forced to sign it. Even if the new landlord is a bank which has foreclosed or even if the it is the government which has ended up with the building, all of the above is true. A new owner can not evict you or raise your rent, except as allowed by Rent Control. By virtue of being a new owner, the new landlord can not evict you.