Make method parameter strongly typed without if/switch

Given a class method can generate report based on the type passed in from method parameter, an easy way to make parameter strongly typed is using enum:

    class ReportGenerator
    {
        string _reportTypeInString;
        enum ReportType
        {
            PDF = 0,
            EXCEL,
            HTML
        }

        void GetReport(ReportType reportType)
        {
            switch (reportType)
            {
                case ReportType.PDF:
                    _reportTypeInString = "PDF";
                    break;
                case ReportType.EXCEL:
                    _reportTypeInString = "EXCEL";
                    break;
                case ReportType.HTML:
                    _reportTypeInString = "HTML40";
                    break;

            }
            // logic to generate real report...
        }
    }

The problem here is: enum type in dotnet only supports integer, converting to string has to be done somewhere usually in a place different than the type define area, maintenance is problematic. Besides, the evil if/switch code smell.

Here is my way to do the same job:

        public class ReportFormat
        {
            public string ReportFormatString { get; private set; }

            public static ReportFormat HTML32 = new ReportFormat("HTML3.2");
            public static ReportFormat HTML40 = new ReportFormat("HTML4.0");
            public static ReportFormat EXCEL = new ReportFormat("EXCEL");
            public static ReportFormat CSV = new ReportFormat("CSV");
            public static ReportFormat PDF = new ReportFormat("PDF");
            public static ReportFormat MHTML = new ReportFormat("MHTML");

            ReportFormat(string reportFormatString)
            {
                ReportFormatString = reportFormatString;
            }
        }

//in my report generator class:
        public FileContentResult GetReport(string reportName, ReportFormat reportFormat, IList<ParameterValue> parameters)
        {...}
// how to use
        var fileContentResult = reportingServiceProxy.GetReport(ReportName, ReportingServiceProxy.ReportFormat.HTML40, parameters);

Work amount is almost same, the type maintenance is in same place, the biggest selling point, no evil if/switch statement anymore.

Which design pattern is used here?