I hope you find them useful

using System.Globalization;

// gets a CurrentYear Julian Date (ddd) Returns DateTime
// ddd = day number
// 001 = January 1st Current Year
// 365 = December 25 Current Year
public DateTime parseJulianDate(String txt) {
    var year = DateTime.Now.Year;
    var days = int.Parse(txt);

    var time = new DateTime(year, 1, 1).AddDays(days - 1);
    
    return time.ToString("MM/dd/yyyy");
}

// gets a Current Year Julian Date (wwd) Returns DateTime
// ww = Week of the year
// d = Day of the week
// 011 = January First Current Year
public DateTime parseJulianWeeksDays(String txt) {
    var yearw = DateTime.Now.Year;
    var daysw = int.Parse(txt.Substring(2, 1));
    var weeksw = int.Parse(txt.Substring(0, 2));

    var cal = CultureInfo.InvariantCulture.Calendar;

    var timew = new DateTime(yearw, 1, 1);
    timew = cal.AddWeeks(timew, weeksw - 1);
    timew = cal.AddDays(timew, daysw - 1);
    
    return timew.ToString("MM/dd/yyyy");
}