how we can add digital signature in pdf using ASP .net core MVC?

You can use LEADTOOLS PDF Pro SDK technology inside your application.

https://www.leadtools.com/sdk/products/pdf-pro

You can leverage the PDFFile class, which will allow you to add a digital signature certificate to a PDF file. Note that you can leverage the PDFDocument class to parse digital signatures with LEADTOOLS as well.

 

I know you stated that you are using ASP.NET Core, so the .NET tutorial below should provide the code on how to digitally sign PDFs.

https://www.leadtools.com/help/sdk/v22/tutorials/dotnet-console-add-a-digital-signature-to-a-pdf.html

Spire.PDF for .NET supports to digitally sign a PDF in C#. Here is an article for your reference.

 

https://www.e-iceblue.com/Tutorials/Spire.PDF/Spire.PDF-Program-Guide/Security/How-to-Digitally-Sign-PDF-with-Timestamp-Server-in-C-VB.NET.html