This post is fairly technical in nature, but also fairly accessible.
Inter-app communication is still in its infancy. Indeed, as powerful software publishers would have it, each app or each suite of apps would attempt to lock users into a unique file format to achieve a sort of monopole. This is clearly what Microsoft was doing in the 90s with MS Office. Since then, the strong competitive and market forces got the best of the crypted files – Microsoft eventually gave way and started allowing a “clear” version of their files (.docx, .xlsx, .pptx), and even published the specifications of their native files (see the Microsoft Open Specification Promise).