I'm looking for free program that allows to extract video, audio or subtitles from
MKV file separately. I'm using Windows 10 Pro (x64) on my desktop.
Can you suggest program that have such functionality and will work on Windows 10 x64?
FFMPEG can do what you need, and a lot more, from the command line under Windows, OS-X & Linux. It is free, gratis & open source.
Because it is so powerful you will probably have to spend some time reading the documentation but from a given input file you can specify which video, audio and subtitle streams you wish to output, in what format.
There are a number of GUI interfaces for FFMPEG but they do limit what you can do, (sometimes sensibly), and quite a few programs use FFMPEG as a back end to do the heavy lifting.