Panama is essentially bi-monetary.
The national official currency is the Balboa (PAB) since 1904. This is pegged to the USD 1:1 by government decision.
Panama only issues coins from B/$0.01 up to B/$1. No banknotes.
Panama has never had a central bank - which is fairly unique as it does have its own currency unlike say Andorra, Tuvalu or Monaco. The government does have an organism that regulates the banking sector however.
The USD also has status as an official currency - "uso legal" vs "curso legal".
Individuals and businesses can choose in which currency they hold accounts, loans, contracts etc - although by default most products are in USD except when dealing with state owned banks or government entities when it will almost always be done in PAB (incase one day they ever decide to unpeg the current exchange rate, as is the country's right.)
If you sign up for a PAB credit/ bank card, when you go to use it in the USA you can expect to see foreign currency fees.
As far as banknotes goes, USD is universally accepted as it is 1:1 and there is no other alternative in wide circulation. With the PAB coins, there is always exact change to be had - think I still have a little bag full of it somewhere.