Trexo PDF Signer is a free and open-source desktop application that allows you to digitally sign PDF documents with legal validity. The program operates entirely on the local machine without needing to upload files to the cloud or pay monthly subscriptions. It is designed for professionals and companies that require real cryptographic signing using X.509 certificates, USB cryptographic tokens, smart cards, or PFX/P12 certificate files. The generated signatures are compatible with Adobe Acrobat Reader and comply with legal standards in most jurisdictions.