test.cs

public class DictionaryController : ApiController
{
    // returns all user dictionaries in the specific folder
    [System.Web.Http.HttpGet]
    public HttpResponseMessage UserDictionaryFilenames()
    {
        var sFilenames = System.IO.Directory
            .EnumerateFiles(System.Web.Hosting.HostingEnvironment.MapPath("~/Dictionaries/"),
              "*.txd", System.IO.SearchOption.TopDirectoryOnly)
            .Select(System.IO.Path.GetFileName); 

        return new HttpResponseMessage()
        {
            StatusCode = HttpStatusCode.OK,
            Content = new ObjectContent<string[]>(sFilenames.ToArray(),
                new JsonMediaTypeFormatter())
        };
    }

    // loads a specific dictionary by filename
    [System.Web.Http.HttpGet]
    public HttpResponseMessage LoadUserDictionary(string filename)
    {
        UserDictionary userDictionary = new UserDictionary() {
            language = "en-US",
            name = filename
        };

        // read all lines from the dictionary
        string[] sDictionaryLines = System.IO.File.ReadAllLines(
          System.Web.Hosting.HostingEnvironment.MapPath("~/Dictionaries/" + filename));

        // skip the first entry (encoding)
        userDictionary.words = sDictionaryLines.Skip(1).ToArray();

        // return the object
        return new HttpResponseMessage()
        {
            StatusCode = HttpStatusCode.OK,
            Content = new ObjectContent<UserDictionary>(userDictionary,
                new JsonMediaTypeFormatter())
        };
    }

    // saves a specific dictionary
    [System.Web.Http.HttpPost]
    public HttpResponseMessage SaveUserDictionary([FromBody] UserDictionary dictionary)
    {
        // get all words and save the dictionary
        List<string> dictionaryLines = new List<string>();
        dictionaryLines.Add("SET iso-8859-1");
        dictionaryLines.AddRange(dictionary.words);

        System.IO.File.WriteAllLines(System.Web.Hosting.HostingEnvironment.MapPath(
          "~/Dictionaries/" + dictionary.name), dictionaryLines);

        return new HttpResponseMessage()
        {
            StatusCode = HttpStatusCode.OK,
            Content = new ObjectContent<string>("UserDictionary " + 
              dictionary.name + " successfully saved.", new JsonMediaTypeFormatter())
        };
    }
}