I'm building a web application that most allow the user to digitally sign PDF documents with certificates installed in the client machine.
The document, once signed, should be posted back to the server, where it will store the signed version.
The server is running Classic ASP/ASP.NET
Where should I go?
I actually built a system just like this into our web application. Here are some links I found tremendously helpful in doing so:
http://www.codeproject.com/KB/vb/Digital_Signatures.aspx
http://www.devx.com/security/Article/17249/0/page/2
http://www.example-code.com/vbdotnet/digSig1.asp
Look for java libraries to sign PDF documents. You can deploy them in an applet which should fit in your web application. If users need to preview the PDF documents before signing them then look at the java bean jPDFNotes from Qoppa Software. If the documents can be signed without preview, look at their other libraries jPDFFields or jPDFProcess. There is also iText an open source library but iText doesn't support viewing documents so it will only work in the second scenario.
Try Adobe LiveCycle Designer
This comes with the Adobe Master Suit and has all the capabilities for ES. It works with PKI infrastructure and will Publish "certified" PDF documents that prove authenticity for recipients. It's better to start with something that already exists.
I would use iTextSharp to sign the PDF. iTextSharp is free and open source. Take a look at the sample code signing PDF http://itextpdf.sourceforge.net/howtosign.html I have used iTextSharp before reliably.
I use to write the FDF to PDF programming from Adobe FDF toolkit. I could take the full version of Acrobat Pro and use a W-2 , I-9 Federal Forms place fields and a signature box and with Topaz Systems signature pads, based on pressure points, angles etc... the activex algorithm would save the signature and everything into the sql server database, and i could go the other way and populate a PDF from SQL Server.
Our SecureBlackbox library has a distributed cryptography add-on which does what you need. Client-side modules that do signing can be extended by the user (we provide complete source code). You will find detailed description of the add-on on our site or in this SO answer.
Seems relatively easy to do this.
You can allow users to download the PDF document.
Users can open the document in Adobe Reader and sign them (not sure if this covers your concept of "signing" the PDF).
Users can then upload the document, which you can then inspect for signatures. Seems like a relatively simple process.
Go to http://www.certisign.com.br/ they have the answer for you. CertSign has API's and training to enable digital certification.
This place did exactly what you need when I renewed my digital CPF http://loja.certificadodigital.com.br/Serasa/Serasa-Certificados-Digitais/D1
We do this using Silverlight with BouncyCastle in the client and iTextSharp in the server.
来源：https://stackoverflow.com/questions/2147732/how-to-digitally-sign-pdf-documents-in-a-web-application