This assumes that you have already copied an mp3 file into your unrealBook documents folder via AirDrop, Email, iTunes or Dropbox/Box.
If you don’t know how to import a file, see importing files.
Go to the CD/Music menu and choose Music Controller.
Press Link Audio File (in Blue).
Choose the mp3 (or mp4) song you want to link to the page. You can use the search field to find the file. Press the title to select the song.
Next, go into the CD/Music menu again and choose Player Volume.
Set the slider to the volume you want for this song and then press Set Volume For Page.
Now when you choose this file and turn to the page and press play, the file will play at the predefined volume. Once a volume level has been saved, the window will display the volume level saved with the page.
If you have iTunes library songs, you will need to enable system volume.
Go to settings->global->Playback and enable System volume slider control.
You will be prompted to quit unrealBook. Double-press Home button or swipe up from the bottom to see the multi-tasking card view. Swipe up on unrealBook. Then run unrealBook again.
Now you can set volumes per page for iTunes library linked songs.