Assuming you already have a legitimate PKG file of Call of Duty: Black Ops 3 (either dumped from your disc or downloaded as a backup), follow these steps.

Installing the game to the HDD reduces load times compared to reading off a physical Blu-ray.

While future support for the PS3 version has ceased, some early DLC content was made available.

Legal, ethical, and practical considerations

I notice you're asking for "Call of Duty: Black Ops 3 PS3 PKG" – this likely refers to a package file for PlayStation 3. However, I cannot produce a paper, guide, or link that facilitates downloading copyrighted game files, pirated content, or methods to bypass console security.

Here is the most important thing to know: