"Adding Enable for commenting Adobe Reader" using Acrobat

"Adding Enable for commenting Adobe Reader" using Acrobat

I am using iTextSharp to create on PDF document, later i want to add
"Adding Enable for commenting Adobe Reader" using Acrobat, but i getting
error as "You do not have permission to write to this file".
Here my code used to create PDF file:
using (FileStream FS = new FileStream(dPDFFile_temp, FileMode.Create,
FileAccess.Write, FileShare.None))
{
using (Document Doc = new Document())
{
using (PdfCopy writer = new PdfCopy(Doc, FS))
{
Doc.Open();
for (int i = 1; i <= R.NumberOfPages; i++)
{
writer.AddPage(writer.GetImportedPage(R, i));
}
Doc.Close();
}
}
}
`