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I would like your opinion on whether something like this is possible or not.

1)Client logs in and uses a webform to submit data. The data is then used to generate a PDF with a digital signature of the client's name and location and is then sent to our server. (i think this step is possible based on what i have read so far.Please correct me if i am wrong)

2)At some point later is it possible to pro-grammatically add additional content to the same pdf(perhaps in a different block) and then add another signature to the pdf?

Thanks! Any samples or examples achieving the same would be great as well.

cableload
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1 Answers1

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The most critical point is

to programmatically add additional content to the same pdf(perhaps in a different block) and then add another signature to the pdf?

To do this without causing signature verifiers, in particular Adobe Reader, to consider the existing signature broken, you have to restrict your changes to those considered allowed for the signature type in question. For a listing of allowed changes look at this answer.

At best, therefore, you are allowed to:

  • Add signature fields
  • Add or edit annotations
  • Supply form field values
  • Digitally sign

(Supplying form field values includes instantiating page templates. Thus, if you prepare the pdf accordingly, you can even add new pages with content prepared but hidden in the originally signed pdf. Preparing page templates and instantiating them is not explicitly supported by all pdf libraries, though. Itext allows this only using low level api tricks.)

mkl
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  • so lets say, i have hidden form field in the pdf that i want to add a text to it later, and then a signature field, it should work isnt it? Are there any samples out there using itextsharp? – cableload Sep 26 '18 at 21:23
  • @cableload Un-hiding a hidden form field might not be allowed after signing, but filling an empty one may be allowed. You might be interested in reading the [Digital Signatures for PDF Documents](https://developers.itextpdf.com/books#digsig) whitepaper by iText. – mkl Oct 25 '18 at 08:25
  • @cableload Did this sufficiently answer your question? – mkl Oct 31 '18 at 17:48