Is there an offline mode in Spotify?
Yes, there is an offline mode that can be activated on PC. To do this, log-in to Spotify and locate the Playlists on the left menu. Right-click a Playlist and choose Available Offline. After this procedure, Spotify will make sure that the files are stored on PC, then if you lack Internet access, Spotify will play those files from the playlists.
To find more about it, use: https://webplayersupport.spotify.com/us/learn-more/guides/#!/article/Listen-offline