iTextSharp in asp.net

there are some examples(some has codes, some has not) that show the usage of iTextSharp in asp.net
http://aspspider.net/tonyfox/pdf/
https://blog.rubypdf.com/2006/10/25/itextsharpitext-example-in-aspnet/
Fill, sign and Save PDF Form online, only Adobe Reader is OK
“Cannot access a closed Stream”(there are some very useful code when use iTextSharp in asp.net)