The plugin
PianoFlex Player is also a plugin, so you can play Session Player inside your music program (often called a DAW) on Windows. The plugin is in the VST3 format, which most music programs on Windows use.
Installing it
The plugin is installed with PianoFlex Player's own installer, from flexmusiclabs.com/pianoflex-player. It goes in Windows' shared folder for VST3 plugins, where every music program looks: C:\Program Files\Common Files\VST3. The PianoFlex Player that comes with ComposerFlex doesn't include the plugin.
Leave the plugin ticked when you install. If your music program doesn't find PianoFlex Player by itself, ask it to scan for new plugins. You'll find it as PianoFlex Player, an instrument from Flex Music Labs.
Using it
Add PianoFlex Player to an instrument track, and play the track from your MIDI keyboard or from the track's MIDI notes. Your music program sends the notes, so the plugin's window has no MIDI in or Output.
The plugin's window has the Player's Room and Volume, the keyboard and the pedals. Your music program keeps the room and the volume with your project, so they're as you left them when you open it again.
Opening MIDI files, rendering and making videos are for the PianoFlex Player program, not the plugin. Your music program renders the track itself.
For more pianos in your music program, and every slider to shape them, there's PianoFlex, our full piano program, with a plugin of its own.