Is there a way to combine PDF files into pdf.js?

Question

Well, I want to combine existing pdf files in html5 using pdf.js and create one pdf file from them

Is it possible and how can I do it?

Answer 1

Combining several documents and simply displaying them as one with pdf.js is easy - I just hacked the following example based on the simple prev / next viewer that mozilla provides in its repository.

    // If absolute URL from the remote server is provided, configure the CORS
    // header on that server.
    //
    var urls = [
        'http://mozilla.imtqy.com/pdf.js/web/compressed.tracemonkey-pldi-09.pdf',
        'http://mozilla.imtqy.com/pdf.js/web/compressed.tracemonkey-pldi-09.pdf'
    ];

    // Disable workers to avoid yet another cross-origin issue (workers need
    // the URL of the script to be loaded, and dynamically loading a cross-origin
    // script does not work).
    //
    // pdfjsLib.disableWorker = true;

    // In cases when the pdf.worker.js is located at the different folder than the
    // pdf.js one, or the pdf.js is executed via eval(), the workerSrc property
    // shall be specified.
    //
    // pdfjsLib.workerSrc = 'pdf.worker.js';

    /**
     * @typedef {Object} PageInfo
     * @property {number} documentIndex 
     * @property {number} pageNumber
     */

var pdfDocs = [],
    /**
     * @property {PageInfo}
     */
    current = {},
    totalPageCount = 0,
    pageNum = 1,
    pageRendering = false,
    pageNumPending = null,
    scale = 0.8,
    canvas = document.getElementById('the-canvas'),
    ctx = canvas.getContext('2d');

/**
 * Get page info from document, resize canvas accordingly, and render page.
 * @param num Page number.
 */
function renderPage(num) {
    pageRendering = true;
    current = getPageInfo(num);
    // Using promise to fetch the page
    pdfDocs[current.documentIndex]
    .getPage(current.pageNumber).then(function (page) {
        var viewport = page.getViewport(scale);
        canvas.height = viewport.height;
        canvas.width = viewport.width;

        // Render PDF page into canvas context
        var renderContext = {
            canvasContext: ctx,
            viewport: viewport
        };
        var renderTask = page.render(renderContext);

        // Wait for rendering to finish
        renderTask.promise.then(function () {
            pageRendering = false;
            if (pageNumPending !== null) {
                // New page rendering is pending
                renderPage(pageNumPending);
                pageNumPending = null;
            }
        });
    });

    // Update page counters
    document.getElementById('page_num').textContent = pageNum;
}

/**
 * If another page rendering in progress, waits until the rendering is
 * finished. Otherwise, executes rendering immediately.
 */
function queueRenderPage(num) {
    if (pageRendering) {
        pageNumPending = num;
    } else {
        renderPage(num);
    }
}

/**
 * Displays previous page.
 */
function onPrevPage() {
    if (pageNum <= 1) {
        return;
    }
    pageNum--;
    queueRenderPage(pageNum);
}
document.getElementById('prev').addEventListener('click', onPrevPage);

/**
 * Displays next page.
 */
function onNextPage() {
    if (pageNum >= totalPageCount && current.documentIndex + 1 === pdfDocs.length) {
        return;
    }
    
    pageNum++;
    queueRenderPage(pageNum);
}
document.getElementById('next').addEventListener('click', onNextPage);

/**
 * @returns PageNumber
 */
function getPageInfo (num) {
    var totalPageCount = 0;
    for (var docIdx = 0; docIdx < pdfDocs.length; docIdx++) {
        
        totalPageCount += pdfDocs[docIdx].numPages;
        if (num <= totalPageCount) {
            return {documentIndex: docIdx, pageNumber: num};
        }
        num -= pdfDocs[docIdx].numPages;
    }
    
    return false;
};

function getTotalPageCount() {
    var totalPageCount = 0;
    for (var docIdx = 0; docIdx < pdfDocs.length; docIdx++) {
        totalPageCount += pdfDocs[docIdx].numPages;
    }
    return totalPageCount;
}

var loadedCount = 0;
function load() {
    // Load PDFs one after another
    pdfjsLib.getDocument(urls[loadedCount]).then(function (pdfDoc_) {
        console.log('loaded PDF ' + loadedCount);
        pdfDocs.push(pdfDoc_);
        loadedCount++;
        if (loadedCount !== urls.length) {
            return load();
        } 
        
        console.log('Finished loading');
        totalPageCount = getTotalPageCount();
        document.getElementById('page_count').textContent = totalPageCount;

        // Initial/first page rendering
        renderPage(pageNum);
    });        
}

<!DOCTYPE html>
<html>
    <head>
        <base href="https://mozilla.imtqy.com/pdf.js/" />
        <meta charset="UTF-8">
        <title>Previous/Next example</title>
    </head>
    <body onload="load()">

        <div>
            <button id="prev">Previous</button>
            <button id="next">Next</button>
            &nbsp; &nbsp;
            <span>Page: <span id="page_num"></span> / <span id="page_count"></span></span>
        </div>

        <div>
            <canvas id="the-canvas" style="border:1px solid black"></canvas>
        </div>

        <script src="build/pdf.js"></script>

    </body>
</html>

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, CORS-, . , , , , , urls.

Answer 2

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