iTextSharp.LGPLv2.Core is an unofficial port of the last LGPL version of the iTextSharp (V4.1.6) to .NET Core.
To install iTextSharp.LGPLv2.Core, run the following command in the Package Manager Console:
PM> Install-Package iTextSharp.LGPLv2.Core
You can also view the package page on NuGet.
You have three license choices when it comes to iTextSharp: LGPL/MPL, AGPL, or a commercial license. The LGPL/MPL license is only an option with the older 4.1.6 version (used here). After that version, they switched to a dual AGPL/Commercial.
If you need a more recent version, you either have to make your project open-source or pay the license fee.
To run this project on Linux, you will need to install libgdiplus too:
sudo apt-get update
sudo apt-get install libgdiplus