Start Reaper and choose "Open" from the "File" menu to load the project containing the individual MIDI region you want to save. In Reaper's Edit Area, locate that MIDI region within your project. Right-click on the region and select "Open items with built-in MIDI editor" from the "Open items in editor" sub-menu. Reaper's MIDI editor will open and display the MIDI data contained in the region.
Right-click in the area at the top of the of the MIDI area next to the "Snap to grid" button. A contextual menu will appear. In the "File" sub-menu, select "Export to new MIDI file." A dialogue box titled "Create new MIDI file" will appear. Name the MIDI file and select a location to save it from the drop-down menu.
Click "Save." Reaper will save a copy of the region as a standard MIDI file in the specified location. You can now open and edit the selected MIDI region as a separate file in the MIDI editor of your choice.
Open the project whose MIDI data you want to save. Open the "File" menu and select "Export project MIDI." A dialogue box titled "Consolidate MIDI" will appear. It contains a number of options for saving your project's MIDI data. To save all of the MIDI data in your project, select "Entire project" under "Consolidate time."
Choose an output format for your MIDI file. If your project contains more than one track with MIDI data, you have the option of preserving the different tracks in the new MIDI file or merging all MIDI data into a single track. For example, if you want to open the new MIDI file in a different multitrack editor, choose the "Multitrack MIDI file" option under "Output to MIDI file." If you want all of the project's MIDI data consolidated onto a single track, select "Merge to single MIDI track."
Specify a location for Reaper to save the new MIDI file by clicking the "Browse" button and navigating to your desired location. Name your MIDI file when prompted and click "OK." Reaper will export and save the MIDI data you specified as a new standard MIDI file in the specified location. It can now be opened in the MIDI editor of your choice.