Getting illegal character after replacing a string through pdfbox

Question

I've followed this answer and wrote program,In pdf I'm trying to replace word datalog with ddddddd.All the occurrence got successfully replaced.But the problem is that at some places where "- " is present got replaced by illegal character Å’.The word datalog is in page no 3,5.But the i got this illegal character at page no 4.I want to know why did i get that character.any help would be highly appreciated.

import java.io.*;
import java.util.*;

import org.apache.pdfbox.cos.COSArray;
import org.apache.pdfbox.cos.COSString;
import org.apache.pdfbox.contentstream.operator.Operator;
import org.apache.pdfbox.pdfparser.PDFStreamParser;
import org.apache.pdfbox.pdfwriter.ContentStreamWriter;
import org.apache.pdfbox.pdmodel.PDDocument;
import org.apache.pdfbox.pdmodel.PDPage;
import org.apache.pdfbox.pdmodel.PDPageTree;
import org.apache.pdfbox.pdmodel.common.PDStream;
import org.apache.pdfbox.pdmodel.font.PDFont;
import org.apache.pdfbox.pdmodel.font.PDTrueTypeFont;

public class SimpleReplace {

    public static void main (String[] args) throws Exception {

        PDDocument document = null;
        String fileName ="";
        try {
            document = PDDocument.load( new File(fileName),"" );
            document.setAllSecurityToBeRemoved(true);

            String outputFileName = "SimpleReplace.pdf";
            // the encoding will need to be adapted to your circumstances
            //String encoding = "ISO-8859-1";
            String encoding = "ISO-8859-1";

            // Note that search and replace can be regular expressions
            // replace all occurrences of 'Hello'
           searchReplace("    ", "Aaaa Aaaaa Aaa", encoding,true, document);
            // replace only first occurrence of 'World'
            // Save the results and ensure that the document is properly closed
            document.save(outputFileName);
        }
        finally {
            if( document != null ) {
                document.close();
            }
        }

    }

    private static void searchReplace (String search, String replace,String encoding ,boolean replaceAll, PDDocument doc) throws IOException {
        PDPageTree pages = doc.getDocumentCatalog().getPages();
        for (PDPage page : pages) {
              int count=0;
            PDFStreamParser parser = new PDFStreamParser(page);
            parser.parse();
            List tokens = parser.getTokens();
            for (int j = 0; j < tokens.size(); j++) {
                Object next = tokens.get(j);
                if (next instanceof Operator) {
                    Operator op = (Operator) next;
                    // Tj and TJ are the two operators that display strings in a PDF
                    // Tj takes one operator and that is the string to display so lets update that operator
                    if (op.getName().equals("Tj")) {
                        COSString previous = (COSString) tokens.get(j-1);
                        String string = previous.getString();
                        if (replaceAll) {
                            string = string.replaceAll(search, replace);

                        }
                        else
                            string = string.replaceFirst(search, replace);
                        previous.setValue(string.getBytes());
                    } else if (op.getName().equals("TJ")) {
                        COSArray previous = (COSArray) tokens.get(j-1);
                        for (int k = 0; k < previous.size(); k++) {
                            Object arrElement = previous.getObject(k);
                            if (arrElement instanceof COSString) {
                                COSString cosString = (COSString) arrElement;
                                String string = cosString.getString();
                                if (replaceAll)
                                    string = string.replaceAll(search, replace);
                                else
                                    string = string.replaceFirst(search, replace);
                                cosString.setValue(string.getBytes());
                            }
                        }
                    }
                }
            }
            // now that the tokens are updated we will replace the page content stream.
            PDStream updatedStream = new PDStream(doc);
            OutputStream out = updatedStream.createOutputStream();
            ContentStreamWriter tokenWriter = new ContentStreamWriter(out);
            tokenWriter.writeTokens(tokens);
            out.close();
            page.setContents(updatedStream);
        }
    }
}