How can Find the number of Pages in a pdf file.

Question

hi all,

i am using
PdfReader pdfr = new PdfReader(strFilePath);
TextBox1.Text = pdfr.NumberOfPages.ToString();

but my problem is that ,  it capture page number of some pdf file and some time it does not capture the page number. I am using itextsharp.dll
plese give some solutation. its urgent

Thanks in Advance.