If you are a Java or .NET developer, all the following articles are useful for you.
if you just want a free Digitally sign PDF tool, try the following ones:
- PortableSigner-Tool to sign Portable Document Files (PDF)
- E-signing PDF documents with iTextSharp
- Sign PDF online, but do not know how to use it
- OpenSignPdf, project of OpenSignature , in Java, to make signed pdf
- One of my work for a RAC buyer,
Merge XFDF to PDF Form ,Do Digital Signature then send to customer
OpenSignature is an open source project for the digital signature of documents. It works with all cards supported by OpenSC and focuses on adding support for cards from accredited Italian CAs. The goal of the project is to provide a first single product capable of supporting cards from multiple vendors/countries. This contrasts the approach taken by card vendors/providers whose software follows an exclusive single-vendor approach. OpenSignature thus attempts to make a major contribution to interoperability in the digital signature domain and aims to greatly facilitate the setup of public access points that are currently the objective of several projects in Italy. Moreover, we hope that the peer-review of the open source approach will allow us to at least match the security level of competing single-card software.