Hi luca,
Thanks for contacting Syncfusion support.
We do not have support for EJ1 PDF Viewer in the ASP.NET core platform. So, we request you to upgrade the EJ2 component to support the PDF Viewer in ASP.net core. Kindly refer to the documentation and online demo from the below links,
Please let us know if you have any concerns about this.
Regards,
Vasugi