title: Traverse whole PDF and change some attribute with some object in it using iText
body: <p>I'm working on a filter program which turns each black text block into gray ones in a PDF file. I have gone through com.itextpdf.text.pdf.parser and can't found something suitable for this function.</p>
  
  <p>PS:
  I'm using iTextSharp 5.5.10, for which I can't find an appropriate document. Documents for iText5 seems to work at most times, but there's still difference. Is there any document for iTextSharp?</p>