When trying to create documents simultaneously from different threads (in concurrent scenario), different exceptions are thrown: - NullReferenceException in Telerik.Windows.Documents.Core.Fonts.OpenType.OpenTypeFontSource.ReadTableData[T](UInt32 tag, ReadTableFormatDelegate`1 readTableDelegate) method, - OverflowException in Telerik.Windows.Documents.Core.Fonts.OpenType.Tables.CMapFormat4Table.Read(OpenTypeFontReader reader) method. Available in LIB version: 2017.2.814