Word Perfect for Linux reads and writes all versions of WP and Microsoft Word files, so you don't have to change anything. In short, almost all the programs you actually use, as opposed to operating system modules you barely notice, are available for free software. If there are so many versions of f.i. I guess I didn't get the RFC protocol, and am experiencing FUD at this moment. So if you don't like, for example, one window manager, there will be others you can choose which may work differently in ways you like better, but which will relate to all surrounding programs in the same predictable and effective ways.
All programs use standard kinds of data, and can exchange that data freely.
Programmers like interoperability, which you call compatibility. They can't always achieve it with proprietary software, because manufacturers don't disclose how their programs work. Microsoft won't tell you how Microsoft Word files are put together, for example, unless you pay them money and promise not to reveal the information. But where all software is freely modifiable, all programs can be made to work together pretty easily. Incompatibility is a problem of the old world, not the new one.