winforms - How to split every pages of a pdf into multiple pdf files in C# (using iTextSharp)? -

i trying convert every pages of pdf separate pdf files. have given range of 6 create 6 separate pdf files.

using system; using itextsharp.text; using itextsharp.text.pdf; using system.windows.forms; using system.io;  namespace learning.spitpdfapp {     public partial class mainform : form {         public mainform() {             initializecomponent();         }          private void splitpdfbutton_click(object sender, eventargs e) {             mainform objmainform = new mainform();             objmainform.extractpage(sourcetextbox.text, destinationtextbox.text);         }          public void extractpage(string sourcepath, string outputpath) {             int startpage = 1;             pdfreader objreader = new pdfreader(sourcepath+".pdf");             int endpage = 6;             document objdocument = new document(objreader.getpagesizewithrotation(startpage));              objdocument.open();              (int index = startpage; index <= endpage; index++) {                 pdfcopy pdfcopyprovider = new pdfcopy(objdocument, new filestream(outputpath+""+index+".pdf", filemode.create));                 pdfimportedpage importedpage = pdfcopyprovider.getimportedpage(objreader, index);                 pdfcopyprovider.addpage(importedpage);             }             objdocument.close();             objreader.close();             messagebox.show(@"splitting successful!");         }     } } 

but throwing null reference pointer exception. can't figure out problem i've caused.

any appreciated. in advance.

this extracts page without exception.

public void extractpage(string sourcepdfpath, string outputpdfpath, int pagenumber)             {                 pdfreader reader = null;                 document document = null;                 pdfcopy pdfcopyprovider = null;                 pdfimportedpage importedpage = null;                  try                 {                     // intialize new pdfreader instance contents of source pdf file:                     reader = new pdfreader(sourcepdfpath);                      // capture correct size , orientation page:                     document = new document(reader.getpagesizewithrotation(pagenumber));                      // initialize instance of pdfcopyclass source                     // document , output file stream:                     pdfcopyprovider = new pdfcopy(document,                         new system.io.filestream(outputpdfpath, system.io.filemode.create));                      document.open();                      // extract desired page number:                     importedpage = pdfcopyprovider.getimportedpage(reader, pagenumber);                     pdfcopyprovider.addpage(importedpage);                     document.close();                     reader.close();                 }                 catch (exception ex)                 {                     throw ex;                 }             }