Ashish,

ashish dhingra wrote:
> Is there any provision in itextsharp,that we can add external computed
> signature in pdf.The scenario is i have computed signature in byte[].i
> want to put that byte[] on pdf using itextsharp.

If I understand you right, you have already created a signature for the
original unprepared PDF file and now want to integrate that signature. In
that case you are out of luck, integrated PDF signatures don't work that
way.

(Well, actually you _could_ by the letter of the ISO 32000-1 specification
add a new revision to that document which contains a signature dictionary
whose ByteRange only encompasses the former revision and whose contents
value is your signature; signing everything but the signature bytes is
merely a recommendation... Adobe Reader/Acrobat and many other programs will
reject such a signature, though. Thus, such integrated signatures would only
be appropriate for very few use cases.)

If on the other hand you merely wanted to express that you have some code
you can throw a pre-calculated digest or a data stream to sign at and as a
response receive a signature, your task might just be feasible: You merely
have to prepare the PDF in question using iTextSharp, apply your code to the
range stream iTextSharp provides (or a hash value of it you calculate),
receive the result, and add it into the Contents of the prepared PDF. As a
starting point, you might want to read chapter 12.4.5 of iText in Action,
2nd edition and look at the various samples for external signing available
on the iText related web sites.

ashish dhingra wrote:
> At time of putting signature,i dont have any information regarding
> signature like:- who signed it,chain info etc.I just have computed hash in
> byte[].

Depending on the kind of signature you have (is it actually a mere encrypted
digest or is it a full-blown signature container?) this might be a big
problem indeed. Some such information either has to be provided while
preparing the PDF or has to be contained in the signature container.

Regards,   Michael.
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