UV-Packer for Blender consists of 2 components that need to be installed separately: The UV-Packer for Blender addon that provides the user interface in Blender and the corresponding program that performs the packing.
This archive contains the add-on for Blender. It can be installed through the Add-ons section in Blender's preferences.
In order to use the packing functionality the UV-Packer for Blender executable must be placed into the same directory the addon is installed into.
You can download the executable at https://www.uv-packer.com/blender/
You can find the documentation for UV-Packer with more information about the installation and usage here: https://doc.uv-packer.com
The addon requires Blender v2.9. UV-Packer exists only for 64 bit Windows (Linux, Apple to be released soon)
For more details, features and updates, check the UV-packer homepage https://www.uv-packer.com