对Node JS使用Hummus（PDF）时，无效字符“�”

Question

我正在尝试在Node JS上使用Hummus来打开pdf，替换字符串并保存一个新的pdf。 问题是当我保存新的pdf时。它不保存“ã”，“õ”，“ê”（UTF-8）之类的字符。我在互联网上找不到任何解决方案，Node JS上关于Hummus的话题很少。

有人可以帮助我吗？

我的代码（来自here）：

const hummus = require('hummus');
const fs = require('fs');

/**
 * Returns a byteArray string
 * 
 * @param {string} str - input string
 */
function strToByteArray(str) {
var utf8 = [];
    for (var i=0; i < str.length; i++) {
        var charcode = str.charCodeAt(i);
        if (charcode < 0x80) utf8.push(charcode);
        else if (charcode < 0x800) {
            utf8.push(0xc0 | (charcode >> 6), 
                      0x80 | (charcode & 0x3f));
        }
        else if (charcode < 0xd800 || charcode >= 0xe000) {
            utf8.push(0xe0 | (charcode >> 12), 
                      0x80 | ((charcode>>6) & 0x3f), 
                      0x80 | (charcode & 0x3f));
        }
        // surrogate pair
        else {
            i++;
            // UTF-16 encodes 0x10000-0x10FFFF by
            // subtracting 0x10000 and splitting the
            // 20 bits of 0x0-0xFFFFF into two halves
            charcode = 0x10000 + (((charcode & 0x3ff)<<10)
                      | (str.charCodeAt(i) & 0x3ff));
            utf8.push(0xf0 | (charcode >>18), 
                      0x80 | ((charcode>>12) & 0x3f), 
                      0x80 | ((charcode>>6) & 0x3f), 
                      0x80 | (charcode & 0x3f));
        }
    }
    return utf8;
}

function replaceText(sourceFile, targetFile, pageNumber, findText, replaceText) {  
    var writer = hummus.createWriterToModify(sourceFile, {
        modifiedFilePath: targetFile
    });
    var modifier = new hummus.PDFPageModifier(writer, pageNumber);
    var sourceParser = writer.createPDFCopyingContextForModifiedFile().getSourceDocumentParser();
    var pageObject = sourceParser.parsePage(pageNumber);
    var textObjectId = pageObject.getDictionary().toJSObject().Contents.getObjectID();
    var textStream = sourceParser.queryDictionaryObject(pageObject.getDictionary(), 'Contents');
    //read the original block of text data
    var data = [];
    var readStream = sourceParser.startReadingFromStream(textStream);
    while(readStream.notEnded()){
        Array.prototype.push.apply(data, readStream.read(10000));
    }
    var string = new Buffer(data).toString().replace(findText, replaceText);

    //Create and write our new text object
    var objectsContext = writer.getObjectsContext();
    objectsContext.startModifiedIndirectObject(textObjectId);

    var stream = objectsContext.startUnfilteredPDFStream();
    stream.getWriteStream().write(strToByteArray(string));
    objectsContext.endPDFStream(stream);

    objectsContext.endIndirectObject();

    writer.end();
}

replaceText('file.pdf', 'output.pdf', 0, /REPLACEME/g, 'My New Custom Text');

对不起，我的英语不好。