In WorksheetPageSetup, you can only get the PageSize, but not set it. The only way is through setting a PaperType.

This is because in Telerik.Windows.Documents.Spreadsheet.Model.Printing.SheetPageSetupBase, the only way to set the pageSize property is by setting a PaperType, then it uses PaperTypeConverter.ToSize(PaperType) to convert it to the pageSize. I cannot see any other way to set this to a custom size set by the user.

Please allow custom page sizing by adding a setter for the PageSize if possible. Thank you!

WorksheetPageSetup pageSetup = worksheet.WorksheetPageSetup;
Size pageSize = new Size(50, 80)
pageSetup.PageSize = pageSize; // produces cs0200
pageSetup.PageSize.Width = pageSize.Width; // produces cs1612
pageSetup.PageSize.Height = pageSize.Height; // produces cs1612