It's proprietary to Adobe Acrobat Reader, which managed to make a name for itself and remain on top of other similar software thanks to continuous development. One of the most popular and safest file types is the Portable Document Format (PDF) and you need specialized applications to be able to access PDF files, let alone create. A computer can be equipped with a whole bunch of different text editors, each with its own set of features for more variety and styles, file support and security.
