public Envelope Extent {get; set;}

{
    //namespace ArcGIS.Desktop.Mapping.Offline
    var extent = MapView.Active.Extent;
    //Check map has sync-enabled content that can be taken offline
    //Note: Run within QueuedTask
    var hasSyncEnabledContent = GenerateOfflineMap.Instance.GetCanGenerateReplicas(map);
    if (hasSyncEnabledContent)
    {
        //Generate Replicas and take the content offline
        //sync-enabled content gets copied local into a SQLite DB
        var gen_params = new GenerateReplicaParams()
        {
            Extent = extent, //SR of extent must match map SR

            //DestinationFolder can be left blank, if specified,
            //it must exist. Defaults to project offline maps location
            DestinationFolder = @"C:\Data\Offline"
        };
        //Sync-enabled layer content will be resourced to point to the
        //local replica content.
        GenerateOfflineMap.Instance.GenerateReplicas(map, gen_params);
    }
}