The correct choice is to configure an HTTP(S) load balancer because it supports both HTTP and HTTPS traffic, allowing for SSL termination. This means it can decrypt the SSL session from the client and forward unencrypted traffic to the backend instances, which is essential for the described application. This approach not only meets the requirement for a single public IP but also enhances performance by offloading SSL encryption/decryption from backend instances.

• Option A is incorrect as an internal TCP load balancer is unsuitable for public applications and does not support SSL termination or HTTP(S) traffic.
• Option B is incorrect because a TCP proxy load balancer does not support SSL termination or HTTP(S) traffic, failing to meet the application's requirements.
• Option C is incorrect since an SSL proxy load balancer is designed for non-HTTP(S) traffic, making it incompatible with the HTTP-based PDF merging application.

For more details, refer to Google Cloud Load Balancing Overview.