我如何将字符串传递给方法词干串和下面给出的方法

Question

// THIS IS STRING BY USING WHICH I AM EXTRACTING ALL TEXT FROM PDF FILE
string t = ExtractAlTextFromPdf(inputFile);

...

public static string ExtractAlTextFromPdf(string inputFile)
{
    //Sanity checks
    if (string.IsNullOrEmpty(inputFile))
        throw new ArgumentNullException("inputFile");
    if (!System.IO.File.Exists(inputFile))
        throw new System.IO.FileNotFoundException("Cannot find inputFile", inputFile);

    //Create a stream reader (not necessary but I like to control locks and permissions)
    using (FileStream SR = new FileStream(inputFile, FileMode.Open, FileAccess.Read, FileShare.Read))
    {
        //Create a reader to read the PDF
        iTextSharp.text.pdf.PdfReader reader = new iTextSharp.text.pdf.PdfReader(SR);

        //Create a buffer to store text


        StringBuilder text = new StringBuilder();
        //Use the PdfTextExtractor to get all of the text on a page-by-page basis
        for (int i = 1; i <= reader.NumberOfPages; i++)
        {

            text.Append(PdfTextExtractor.GetTextFromPage(reader, i));
        }

        return text.ToString();
    }
}

//  when i pass this string to method 
public string stem(string word)
{
    if (word.Length < 3) return word;

    StringBuilder sb = new StringBuilder(word.ToLower());

    if (sb[0] == '\'') sb.Remove(0, 1);

    for (int i = 0; i < exceptions.Length / 2; ++i)
        if (word == exceptions[i, 0])
            return exceptions[i, 1];

    int r1 = 0, r2 = 0;
    changeY(sb);
    computeR1R2(sb, ref r1, ref r2);

    step0(sb);
    step1a(sb);

    for (int i = 0; i < exceptions2.Length; ++i)
        if (sb.ToString() == exceptions2[i])
            return exceptions2[i];

    step1b(sb, r1);
    step1c(sb);
    step2(sb, r1);
    step3(sb, r1, r2);
    step4(sb, r2);
    step5(sb, r1, r2);


    return sb.ToString().ToLower();
}

它给出了错误