What is a NUPKG file?
A NUPKG file is a package file that contains source code to be used by NuGet software for creating packages to be used in .NET projects. NuGet Package Manager component is installed as part of Microsoft Visual Studio for fetching packages from online packages hosting repository. NUPKG files help developers fetch the latest packages from Nuget.org using NuGet Package Manager instead of manually downloading and installing the development packages. NUPKG files are built from NUSPEC files and, when fetched, install the package on user system.
NUPKG File Format
NUPKG files are ZIP archives that contain the packaged libraries inside it. When downloaded, it can be renamed to .zip and extracted with any standard zip utilities like WinZIP, 7-Zip, and Apple Archive Utility.