itextsharp - How to stamp and sign a pdf ALREADY signed without invalidating previous signature -

some plugins , programs can this; there example or tutorial how using .net , itextsharp??

i need take signed pdf , stamp imagen on pages , add signature. first signature on document must valid when open file.

thanks in advance.

when require first signature on document must valid when open file, assume foremost talk opening in current adobe reader version.

in case first of must aware allowed , disallowed changes depend on first signature itself. have @ this answer information on "allowed , disallowed changes" considered adobe since version 9 of acrobat & reader.

thus, to take signed pdf , stamp image on pages , add signature , not invalidate (in eyes of adobe software) initial signature in process, signed pdf must

• either uncertified (i.e. initial signature merely approval signature)

• or certified annotations, form fill-in, , digital signatures, allowed (i.e. initial signature certification signature types of changes allowed) , have empty signature field put signature into.

if signed pdf contains multiple signatures, neither of them means of locking information shall have added additional restrictions.

(furthermore assume pdf neither encrypted nor contain dynamic xfa forms; complicate things more.)

if these requirements fulfilled, can use pdfstamper retrieve static pdfstamper method

public static pdfstamper createsignature(pdfreader reader, stream os, char pdfversion, string tempfile, bool append) 

where final bool parameter value must true (i.e. must work in append mode not invalidate initial signature).

using pdfstamper add image on document pages means of annotations. itext in action — 2nd edition sample timetableannotations3.java / timetableannotations3.cs illustrates how add annotations pdfstampers.

then add signature usual, either creating new signature field or using empty one. find details on signing process in whitepaper digital signatures pdf documents; c# samples equivalent java samples in white paper can found here on sourceforge.

ps: stressed in eyes of adobe software in post. when talking certified pdfs adobe pretty near pdf standard here. signed uncertified pdfs adobe applies rules analogous specified certified documents.