Digital Signing PDF - External Signing Use Case

Naman Shah

6y3.8k

I have described my issue below reateld to external and deferred signing

1. We have PDF which I need to digitally sign

2. I will create Hash of PDF which will be sen to Third party service which will sign the hash with private key

3. Third party service will return public key in PEM format and signed hash value

4. Note: Third party will not share the private key

5. I need to sign PDF using above two values

How can I achieve using iText or any other like library in C#.

Can you share sample code which can be used to exactly do this

I have referred multiple links. like below and also created sample (link below). Please help urgently.

Link I have referred so far:

https://stackoverflow.com/questions/47505696/itext-pdf-deferred-signing-results-in-pdf-with-invalid-signature

https://stackoverflow.com/questions/33019686/itext-signing-pdf-using-external-signature-with-smart-card

Based on all this idea I have created some code below. Not sure if my approach is correct. Please help.

I have uploaded my code at - https://1drv.ms/u/s!Al69FgQ8jwmZbgiBMXLLM4j5sbU?e=vyGF4m

The code contains sample PDFs also.

3 Replies

Know the answer? Post it — somebody with the same question will find it here.

Bharat Vasant6y ago
For Web application or Browser based signing, you may refer to complete walk through and sample C# VS 2015 / VS 2017 working project availalbe at https://help.signer.digital/digital_signing_and_authentication_from_web_browser.htm
Naman Shah6y ago
This is case of deferred/external siging. I have asked if the product supports it. I know iText supports it but there is no sufficient samples around it.
Sapna Girish6y ago
Not sure if this solution can meet your requirements, but you could give it a try.

https://www.e-iceblue.com/Tutorials/Spire.PDF/Spire.PDF-Program-Guide/PDF-Protection-Create-Digital-Signature-in-PDF-with-C-VB.NET.html