Sejarah artikel:Balai Sertifikasi Elektronik (BSrE) as one of the Certificate Authorities in Indonesia has been released a desktop-based digital signing application, but one of the weaknesses of desktop applications is its low portability. BSrE has also released a digital signing application for mobile operating systems, but it is only intended for users of the Android operating system. The aim of this research is to develop a digital signing application with Telegram Bot platform, that can be used to sign electronic documents using X509 certificates wherever and whenever, and also it can be run on all operating system platforms. The research methodology is using Rapid Application Development (RAD) which consists of four stages, Requirements Planning, User Design, Construction and Cutover. The backend system of the bot is built using Java programming language, and integrated with the MySQL database as conversation sessions storage. There are three main functions of the designed system, sign, verify and setting. Signed documents also have been tested in several pdf reader applications and digital signatures can be recognized and validated. Bot can also verify documents signed by other applications. Testing uses a black-box method, the results of functional testing and non-functional testing show the system can run properly as expected in requirements planning. Evaluation using System Usability Scale (SUS) indicate that the system is suitable for use.