Does Parallel.ForEach require AsParallel()

ParallelEnumerable has a static member AsParallel. If I have an IEnumerable<T> and want to use Parallel.ForEach does that imply that I should always be using AsParallel?

e.g. Are both of these correct (everything else being equal)?

without AsParallel:

List<string> list = new List<string>();
Parallel.ForEach<string>(GetFileList().Where(file => reader.Match(file)), f => list.Add(f));

or with AsParallel?

List<string> list = new List<string>();
Parallel.ForEach<string>(GetFileList().Where(file => reader.Match(file)).AsParallel(), f => list.Add(f));