Final answer:
The ancient seaport with copyrights to all documents entering it was Alexandria, due to its famous Library of Alexandria which housed an extensive collection of books and knowledge.
Step-by-step explanation:
The ancient seaport which held copyrights to all documents entering into it was Alexandria (A). It was not merely a hub of trade but also a highly esteemed center of knowledge and learning during the Hellenistic period. The city of Alexandria was home to the famous Library of Alexandria, where the Ptolemaic rulers stored and controlled the largest collection of books in the ancient world. This library served as a significant cultural and intellectual repository, and as such, it is likely that copyrights or similar systems of document control would have been in place to protect the vast amount of knowledge contained within its walls.