How to replace text in a pdf with correct encoding using Itext

Question

I create a java program for translating PDFs. I am using google API for translation. I am getting the translation correct on my Eclipse IDE Console but when I check the newly created pdf, either it's not translated and copied as it is or few words are translated or the new pdf comes as empty and sometimes corrupted.

I suppose it has something to do with encoding & font types.

I have already gone through the Itext page & all the related questions but none worked for my case. I am trying to translate Portuguese Spanish Finnish French Hungarian, etc into English.

Here is my code:

public static final String SRC = "5587309Finnish.pdf";  

public static final String DEST = "changed.pdf";


    public static void main(String[] args) throws java.io.IOException, DocumentException {

        Translate translate = TranslateOptions.getDefaultInstance().getService();
        PdfReader reader = new PdfReader(SRC);
        int pages = reader.getNumberOfPages(); 
        PdfStamper stamper = new PdfStamper(reader, new FileOutputStream(DEST));
        for(int i=1;i<=pages;i++) {
        PdfDictionary dict = reader.getPageN(i);

        PdfObject object = dict.getDirectObject(PdfName.CONTENTS);

        if (object instanceof PRStream) {
            String pageContent = 
                    PdfTextExtractor.getTextFromPage(reader, i);
            String[] word = pageContent.split(" ");

            PRStream stream = (PRStream) object;
            byte[] data = PdfReader.getStreamBytes(stream);

              String dd = new String(data, BaseFont.CP1252);


              for (int j=0; j < word.length; j++)
                {

                  Translation translation = translate.translate(word[j],Translate.TranslateOption.sourceLanguage("fi"), 
                          Translate.TranslateOption.targetLanguage("en"));
                 System.out.println(word[j]+"-->>"+translation.getTranslatedText());//here i can check the translation is correct.
                   dd = dd.replace(word[j],translation.getTranslatedText());




                }

              stream.setData(dd.getBytes());


        }
        }

        stamper.close();
        reader.close();

    }

Please help.

Answer 1

According to a comment you have improved your code and are

getting the update dd(i.e. content stream which I am printing) correctly with the replaced text. I don't know why I am getting a blank pdf

Thus, I assume that your (hopefully representative) test PDFs have all their fonts of interest encoded in ANSI'ish encodings and the text arguments of the text drawing instructions contain whole words or even phrases which can properly be processed because otherwise text replacement would not have been possible.

Thus, here an example how one can replace text pieces with similarly long ones under such benign circumstances without breaking the content stream syntax. In this example I simply use a Map containing replacement strings. You can do your translation there.

First a frame loading the source, creating a stamper, iterating over the pages, and calling a helper to create a content stream replacement:

Map<String, String> replacements = new HashMap<>();
replacements.put("Förfallodatum", "Ablaufdatum");

try (   InputStream resource = SOURCE_INPUTSTREAM;
        OutputStream result = new FileOutputStream(RESULT_FILE)  ) {
    PdfReader pdfReader = new PdfReader(resource);
    PdfStamper pdfStamper = new PdfStamper(pdfReader, result);
    for (int pageNum = 1; pageNum <= pdfReader.getNumberOfPages(); pageNum++) {
        PdfDictionary page = pdfReader.getPageN(pageNum);
        byte[] pageContentInput = ContentByteUtils.getContentBytesForPage(pdfReader, pageNum);
        page.remove(PdfName.CONTENTS);
        replaceInStringArguments(pageContentInput, pdfStamper.getUnderContent(pageNum), replacements);
    }
    pdfStamper.close();
}

(EditPageContentSimple test testReplaceInStringArgumentsForklaringAvFakturan)

The method replaceInStringArguments now parses the instructions in the given content stream, isolates string arguments, and calls another helper for each string argument doing the replacement.

void replaceInStringArguments(byte[] contentBytesBefore, PdfContentByte canvas, Map<String, String> replacements) throws IOException {
    PRTokeniser tokeniser = new PRTokeniser(new RandomAccessFileOrArray(new RandomAccessSourceFactory().createSource(contentBytesBefore)));
    PdfContentParser ps = new PdfContentParser(tokeniser);
    ArrayList<PdfObject> operands = new ArrayList<PdfObject>();
    while (ps.parse(operands).size() > 0){
        for (int i = 0; i < operands.size(); i++) {
            PdfObject pdfObject = operands.get(i);
            if (pdfObject instanceof PdfString) {
                operands.set(i, replaceInString((PdfString)pdfObject, replacements));
            } else if (pdfObject instanceof PdfArray) {
                PdfArray pdfArray = (PdfArray) pdfObject;
                for (int j = 0; j < pdfArray.size(); j++) {
                    PdfObject arrayObject = pdfArray.getPdfObject(j);
                    if (arrayObject instanceof PdfString) {
                        pdfArray.set(j, replaceInString((PdfString)arrayObject, replacements));
                    }
                }
            }
        }
        for (PdfObject object : operands)
        {
            object.toPdf(canvas.getPdfWriter(), canvas.getInternalBuffer());
            canvas.getInternalBuffer().append((byte) ' ');
        }
        canvas.getInternalBuffer().append((byte) '\n');
    }
}

(EditPageContentSimple helper method)

The method replaceInString in turn retrieves a single string operand (a PdfString instance), manipulates it, and returns the manipulated string version:

PdfString replaceInString(PdfString string, Map<String, String> replacements) {
    String value = PdfEncodings.convertToString(string.getBytes(), PdfObject.TEXT_PDFDOCENCODING);
    for (Map.Entry<String, String> entry : replacements.entrySet()) {
        value = value.replace(entry.getKey(), entry.getValue());
    }
    return new PdfString(PdfEncodings.convertToBytes(value, PdfObject.TEXT_PDFDOCENCODING));
}

(EditPageContentSimple helper method)

Instead of that for loop here you would call your translation routine and translate value.

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As has been mentioned before, this code only works under certain benign circumstances. Don't expect it to work for arbitrary documents from the wild, in particular not for documents with other than Western European glyphs.