Cannot implicitly convert type ‘System.Collections.Generic.IEnumerable’ to ‘System.Collections.Generic.List

IEnumerable<string> e = (from char c in source
                        select new { Data = c.ToString() }).Select(t = > t.Data);
// or
IEnumerable<string> e = from char c in source
                        select c.ToString();
// or
IEnumerable<string> e = source.Select(c = > c.ToString());

Then you can call ToList():

List<string> l = (from char c in source
                  select new { Data = c.ToString() }).Select(t = > t.Data).ToList();
// or
List<string> l = (from char c in source
                  select c.ToString()).ToList();
// or
List<string> l = source.Select(c = > c.ToString()).ToList();