Aspose PDF and Iron PDF are both PDF generation and manipulation libraries for the .NET framework which are popular with C# developers. Aspose PDF does have a NuGet package named Aspose.PDF. Iron PDF also has a NuGet package. https://ironpdf.com/
The PDF formatted files is not easily editable so PDF insert page numbers is also not so easy so for that you need a third party tool that will help you to insert page numbers in it then try PDF Bates numberer tool which is free to use.