PDF merge failing with .net library

Also in .Net library we couldn’t find a type called pd4document.. but looks like this is available in the java library, as shown here
http://www.pd4ml.com/cookbook/pd4ml_pdf_merge.htm

PD4Document doc1 = new PD4Document(new URL(“file:c:/pdfs/doc1.pdf”), null);  
int pagenum = doc1.getNumberOfPages();  
…  
PD4Document doc2 = new PD4Document(new URL(“file:c:/pdfs/doc2.pdf”), null);  
pagenum = doc2.getNumberOfPages();  
…           
doc2.append(doc1);  
pagenum = doc2.getNumberOfPages();  
…           
File f = new File(“c:/pdfs/result.pdf”);              
FileOutputStream fos = new FileOutputStream(f);  
doc2.write(fos);