The PDF signing is not supported in ASP.NET Core. There is a feature request about this functionality which public link can be followed on this link: https://feedback.telerik.com/document-processing/1432888-pdfprocessing-add-support-for-digital-signature-for-net-standard.
I cannot say when the described feature will be implemented. It all depends on the community interest in it and our priority queue. You can vote for the linked request. The more votes it collects, the bigger the chance for its sooner implementation is. You can also follow the linked item and thus you will be updated when there is a change in its status.
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