Postgres allows the use of any existing database on the server as a template when creating a new database. I'm not sure whether pgAdmin gives you the option on the create database dialog but you should be able to execute the following in a query window if it doesn't:
CREATE DATABASE newdb WITH TEMPLATE originaldb OWNER dbuser;
Still, you may get:
ERROR: source database "originaldb" is being accessed by other users
To fix it you can use this query
SELECT pg_terminate_backend(pg_stat_activity.pid) FROM pg_stat_activity
WHERE pg_stat_activity.datname = 'originaldb' AND pid <> pg_backend_pid();