How do I check a page with roman Numeral

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C#6.0

I have a code that check value of pages.. but now I want the sequence of roman numeral to check. Can some try to edit my code and to make it check the roman numeral pages.

public void CheckPBSequence()
        {
            int pagenoInt;
            List<string> validpage = new List<string>(File.ReadAllLines(string.Concat(AppDomain.CurrentDomain.BaseDirectory, ConfigurationManager.AppSettings["validpage"].ToString())));
            int prevPbNo = 0;
            bool isRoman = false;
            foreach (XElement pb in this._xdoc.Descendants("text").Descendants<XElement>("pb"))
            {
                try
                {
                    string pagenoStr = pb.Attribute("n").Value;
                    if (int.TryParse(pagenoStr, out pagenoInt))
                    {
                        if ((prevPbNo == 0 ? false : pagenoInt != prevPbNo + 1))
                        {
                            List<ErrorModel> errorlist = this.Errorlist;
                            ErrorModel errorModel = new ErrorModel()
                            {
                                LineNumber = ((IXmlLineInfo)pb).LineNumber,
                                ErrorMessage = "Incorrect page number",
                                Text = pagenoStr
                            };
                            errorlist.Add(errorModel);
                        }
                        if (isRoman)
                        {
                            prevPbNo = 0;
                        }
                        isRoman = false;
                        prevPbNo = pagenoInt;
                    }
                    else
                    {
                        if (RomanNumeralUtility.TryConvertToArabic(pagenoStr, out pagenoInt))
                        {
                            if (!isRoman)
                            {
                                prevPbNo = 0;
                            }
                            isRoman = true;
                        }
                        else if (!validpage.Contains(pagenoStr))
                        {
                            List<ErrorModel> errorModels = this.Errorlist;
                            ErrorModel errorModel1 = new ErrorModel()
                            {
                                LineNumber = ((IXmlLineInfo)pb).LineNumber,
                                ErrorMessage = "Incorrect page number",
                                Text = pagenoStr
                            };
                            errorModels.Add(errorModel1);
                        }
                        prevPbNo = 0;
                    }
                }
                catch (NullReferenceException nullReferenceException)
                {
                }
            }
        }