Portable PDF Digital Signature(Portable PdfSigner) Release
Developed in DOTNET(C#), bases on iTextSharp, but compiled with mono, so it can run without .net framework, a really portable version, and it is free
The main feature is,
* Digital Sign a PDF document with PKCS#12 certificates
* Can modify meta data
* Supports multiple signatures.
for detail, please visit
http://blog.rubypdf.com/2009/02/26/portable-pdf-digital-signature-releases/