How can add space\margin between two elements in iTextSharp\iText?

You have a couple of different options. You could set the SpacingAfter on your paragraph:

titolo.SpacingAfter = 20;

You could also set the SpacingBefore on the table:

table.SpacingBefore = 20;

Or you could just add some returns to your paragraph:

iTextSharp.text.Paragraph titolo = new iTextSharp.text.Paragraph("Hello World\n\n");