Currently, Telerik Document Processing is available only for .NET Framework and (partially) for Silverlight. Create version targeting .NET Core.

Update: There is a version of Telerik Document Processing compatible with .NET Core 3.0 in the UI for WPF suite. You can use this version in .NET Core projects running on Windows. The assemblies can be downloaded from telerik.com, the Downloads section of UI for WPF -> Betas tab. Please, note that you should have a valid license for UI for WPF in order to be able to see this version. In case you don't, you can use the Trial license by downloading a trial version of the suite. More information about this version of UI for WPF and how it can be used is available in the related blog post.

When xlsx/docx document is imported, and its main story is with non-default name ('workbook. xml'/'document.xml'), e.g. workbook2.xml/document2.xml, NullReferenceException is thrown and the document is not imported.

Note: Such documents are usually produced after conversion from a template dotx/xlsm.