JSignPdf
Add digital signatures to PDF documents - GUI and CLI, cross-platform
JSignPdf is a free, open-source Java application for signing PDF documents with digital certificates. It provides a graphical desktop interface for everyday users and a command-line mode for scripted and server-side workflows.
Supported capabilities include PKCS#12 keystores, smartcards and hardware tokens (PKCS#11), Windows keystore integration, visible signatures with custom images and positioning, timestamp authority (TSA) support, OCSP/CRL revocation checks, certification signatures, and PDF encryption.
...