how to upload any format file and store as pdf

I want to upload a file and storing as pdf.

in jsp page I have write :

in java action page :

IDfSysObject annexObj = (IDfSysObject) session.newObject("enotesheet_annexure");

annexObj.setString("annex_desc", value);

  annexObj.setString("file_id", file_id);

  // FileBrowse

  FileBrowse fileBrowse = (FileBrowse) getControl("browse",FileBrowse.class);

  String fileName = fileBrowse.getValue();

  // getting the file name

  String fileNames[] = fileName.split("\\\\");

  int len = fileNames.length - 1;

  int a = fileNames[len].indexOf(".");

  String browsedFileName = fileNames[len].substring(0, a);

  annexObj.setObjectName(browsedFileName);

  annexObj.setString("a_content_type","pdf");

  annexObj.setContentType("pdf");

  annexObj.setFile(fileBrowse.getValue());

  annexObj.link("/ENotesheet" + "/" + file_id + "/Annexures");

  annexObj.save();

it is not converting  any file format to another format . How can we achieve it . I am new in documentum.