Since the Google Summer of Code, in collaboration with re-lab, LibreOffice community started to open to the broader free-software ecosystem several proprietary file-formats. This talk will present the libraries for parsing Visio (libvisio), CorelDraw (libcdr) or MS Publisher (libmspub) documents that are currently used by several free-software projects. The talk will focus on interesting details of reverse-engineering, and explain our method of "incremental" reverse-engineering which allowed us to open the file-formats of all CorelDraw versions. The same method is currently used to open the file-formats of all remaining versions of MS Visio. The talk will also present some of the introspection tools we develop and use. Those tools are free-software and their use goes beyond the reverse-engineering work.