This type of action is currently not supported and a NotSupportedActionException is thrown when accessing such an object.

These exceptions can be handled using the Handling Exceptions mechanism.

When merging documents` pages using the PdfStreamWriter the Form Fields are not copied:

using (PdfStreamWriter fileWriter = new PdfStreamWriter(File.OpenWrite(document2Name)))
{
	// Iterate through the files you would like to merge 
	for (int i = 0; i < 2; i++)
	{
		// Open each of the files 
		using (PdfFileSource fileToMerge = new PdfFileSource(File.OpenRead(document1Name)))
		{
			// Iterate through the pages of the current document 
			foreach (PdfPageSource pageToMerge in fileToMerge.Pages)
			{
				// Append the current page to the fileWriter, which holds the stream of the result file 
				fileWriter.WritePage(pageToMerge);
			}
		}
	}
}

A possible workaround is to use the RadFixedDocument`s Merge() method: 

document1.Merge(document2);

I have a simple program that imports a PDF, calls AcroForm.FlattenFormFields(), and calls Export() on the PdfFormatProvider. With the attached example PDF I am seeing the following exception.

System.NotImplementedException: 'The method or operation is not implemented.'

Stack Trace

at Telerik.Windows.Documents.Core.Fonts.Type1.Type1Format.Type1FontSource.GetCapHeight()
   at Telerik.Windows.Documents.Core.Fonts.FontSource.get_CapHeight()
   at Telerik.Windows.Documents.Fixed.FormatProviders.Pdf.Model.Elements.Fonts.FontDescriptor.CopyRequiredButType3FontPropertiesFrom(FontBase font)
   at Telerik.Windows.Documents.Fixed.FormatProviders.Pdf.Model.Elements.Fonts.FontDescriptor.CopyPropertiesFrom(IPdfExportContext context, FontBase font)
   at Telerik.Windows.Documents.Fixed.FormatProviders.Pdf.Model.Elements.Fonts.SimpleFontObject.CopyPropertiesFromOverride(IPdfExportContext context, FontBase font)
   at Telerik.Windows.Documents.Fixed.FormatProviders.Pdf.Export.PdfExporter.WriteFontsFromContext(PdfWriter writer, IPdfExportContext context)
   at Telerik.Windows.Documents.Fixed.FormatProviders.Pdf.Export.PdfExporter.Export(IRadFixedDocumentExportContext context, Stream output)
   at Telerik.Windows.Documents.Fixed.FormatProviders.Pdf.ExceptionHandling.ExecutionHandler.TryHandleExecution[E](Action operation)
   at Telerik.Windows.Documents.Fixed.FormatProviders.Pdf.PdfFormatProvider.ExportOverride(RadFixedDocument document, Stream output)

• Coons patch meshes (type 6) construct a shading from one or more color
  patches, each bounded by four cubic Bézier curves.

Add support for GoToR action

Note: related item: PdfProcessing: Introduce functionality to preserve GoToR actions during import/export