Hi Ayubu,
Thank you for contacting Syncfusion support,
At present we do not have support for PDF viewer in ASP.NET core platform. In PDF viewer, the PDF document data are parsed in the server side and sent to the client for rendering, so the provided code snippet will not work for ASP.NET Core.
We have already added it to our feature request list for “Support for PDF viewer in ASP.NET Core” and it will be available from our Essential Studio Volume 4 release which is expected to be rolled out in the month of December, 2018.
Regards,
Karthik.