Edit table data without primary key

Since the table doesn't have a primary key or OIDs, you can view the data only. Inserting new rows and changing existing rows isn't possible for the Edit Data tool without primary key.

In order to edit data, pgAdmin III requires a primary key on the table, which is a good database design practice anyway. Alternatively, the table can be created WITH OIDS. Please note that oids are not guaranteed to be unique over a very long period of time, so using oids as kind-of primary key is only second choice.