Trexo PDF Signer

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.

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• Signing with PKCS#11 tokens. The program supports a wide variety of hardware security devices such as SafeNet eToken, Gemalto, ProxKey, Feitian, mToken, Watchdata, and any token compatible with the PKCS#11 standard. Communication with the hardware is done directly without proprietary intermediary software.
• Signing with PKCS#12/PFX files. It allows loading password-protected certificate files in PFX or P12 format. The software extracts the private key and certificate to generate the signature without storing sensitive information on the disk.
• Signing with the Windows store. Native integration with the Windows operating system certificate store. Certificates installed in the user's personal container can be selected directly for signing documents.
• RFC 3161 Timestamping. Incorporates timestamping with servers that comply with the RFC 3161 specification. This functionality guarantees the long-term validity of the signature even after the certificate has expired.
• Hash algorithm support. Offers a selection between the SHA-256, SHA-384, and SHA-512 cryptographic algorithms for calculating the document hash. The user can choose the required security level for each signing operation.
• Certificate chain validation. Performs a complete trust chain check using OCSP queries and CRL revocation lists. The software verifies the revocation status of each certificate in the chain before applying the signature.
• Customizable visual appearance. The graphical appearance of the signature can be fully configured. The user can include text with signer data, date, and reason, as well as incorporate images of logos or scanned signatures in PNG or JPEG format.
• Multiple signatures per document. The program allows adding several digital signatures in different positions of the same PDF file. Each signature is applied independently without invalidating the previous existing signatures in the document.
• Drag-and-drop placement. The position of the visual signature is selected directly in the document preview using the drag-and-drop interface. The signature rectangle can be moved and resized with the mouse before applying the signature.
• Integrated signature verification. It has functionality to validate existing signatures in PDF documents. The verification module checks the integrity of the document, the cryptographic validity of the signatures, and the status of the certificates used.
• Native multi-platform. The application works on Windows, Linux, and macOS systems without the need for virtual machines or emulation layers. The specific installer for each platform provides integration with the corresponding desktop environment.
• Offline operation. The entire signing process runs locally without requiring an internet connection. Only OCSP validation queries or CRL list downloads need connectivity, and these can be disabled if total isolation is required.

The development of Trexo PDF Signer began in 2026 as an internal project of Trexolab Solution to cover corporate digital signature needs with cryptographic hardware. The development team is made up of engineers with experience in computer security and applied cryptography. The application is primarily written in the Python programming language, using the Qt framework for the graphical interface and standard cryptographic libraries such as pyca/cryptography and pkcs11. The source code is available under the AGPL-3.0 license, which allows for independent auditing and modification by the technical community.

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