signature

GNU Privacy Guard (GnuPG or GPG) is a free-software replacement for Symantec's PGP cryptographic software suite.

A secure solution for file and email encryption.

Free software for checking signed and sealed documents and time stamps

Sign your PDF documents with ease

Free PGP Encryption Software

A modern, cross-platform, open-source GUI for OpenPGP encryption.

Automatic and centrally managed email signatures for all staff on all devices.

Free PDF viewer, signature editor and highlighter that shows documents as a two page book spread.

A fast, lightweight PDF reader with signing, form filling, and highlighting.

Qualified electronic signature application by Disig

Feature rich iOS/tvOS sideloading application written in Rust.

Synchronize signatures directly with the user's Outlook on Windows.

Sign your documents digitally

Alipay key tool

Free AGPL edition of miPDFsign — a tablet signature app that embeds handwritten signatures with biometric data as PAdES into PDFs.