pdfkit010-with-visual.js

var fs = require('fs');
var path = require('path');
var PDFDocument = require('pdfkit');
var signpdf = require('@signpdf/signpdf').default;
var P12Signer = require('@signpdf/signer-p12').P12Signer;
var pdfkitAddPlaceholder = require('@signpdf/placeholder-pdfkit010').pdfkitAddPlaceholder;

/**
 * Transform coordinates from top/left to bottom/left coordinate system
 */
function topLeftToBottomLeft(coords, page) {
    return [
        coords[0], // x1
        page.height - coords[1], // y1
        coords[2], // x2
        page.height - coords[3], // y2
    ];
}

function addVisual(pdf) {
    // Go to first page
    pdf.switchToPage(0);

    var margin = 30;
    var padding = 10;
    var label = 'Signed with @signpdf';
    pdf
        .fillColor('#008B93')
        .fontSize(10);
    var text = {
        width: pdf.widthOfString(label),
        height: pdf.heightOfString(label)
    };
    text.x = pdf.page.width - text.width - margin;
    text.y = pdf.page.height - text.height - margin;

    pdf.text(label, text.x, text.y, {width: text.width, height: text.height});
    
    return [
        text.x - padding,
        text.y - padding,
        text.x + text.width + padding,
        text.y + text.height + padding,
    ];
}

function work() {
    // Start a PDFKit document
    var pdf = new PDFDocument({
        autoFirstPage: false,
        size: 'A4',
        layout: 'portrait',
        bufferPages: true,
    });;
    pdf.info.CreationDate = '';

    // At the end we want to convert the PDFKit to a string/Buffer and store it in a file.
    // Here is how this is going to happen:
    var pdfReady = new Promise(function (resolve) {
        // Collect the ouput PDF
        // and, when done, resolve with it stored in a Buffer
        var pdfChunks = [];
        pdf.on('data', function (data) {
            pdfChunks.push(data);
        });
        pdf.on('end', function () {
            resolve(Buffer.concat(pdfChunks));
        });
    });

    // Add some content to the page(s)
    pdf
        .addPage()
        .fillColor('#333')
        .fontSize(25)
        .moveDown()
        .text('@signpdf');

    // !!! ADDING VISUALS AND APPLYING TO SIGNATURE WIDGET ==>

    // Add a some visuals and make sure to get their dimensions.
    var visualRect = addVisual(pdf);
    // Convert these dimension as Widgets' (0,0) is bottom-left based while the
    // rest of the coordinates on the page are top-left.
    var widgetRect = topLeftToBottomLeft(visualRect, pdf.page);

    // Here comes the signing. We need to add the placeholder so that we can later sign.
    var refs = pdfkitAddPlaceholder({
        pdf: pdf,
        pdfBuffer: Buffer.from([pdf]), // FIXME: This shouldn't be needed.
        reason: 'Showing off.',
        contactInfo: 'signpdf@example.com',
        name: 'Sign PDF',
        location: 'The digital world.',
        signatureLength: 1612,
        widgetRect: widgetRect, // <== !!! This is where we tell the widget to be visible
    });

    // <== !!! ADDING VISUALS AND APPLYING TO SIGNATURE WIDGET

    // `refs` here contains PDFReference objects to signature, form and widget.
    // PDFKit doesn't know much about them, so it won't .end() them. We need to do that for it.
    Object.keys(refs).forEach(function (key) {
        refs[key].end()
    });

    // Once we .end the PDFDocument, the `pdfReady` Promise will resolve with
    // the Buffer of a PDF that has a placeholder for signature that we need.
    // Other that we will also need a certificate
    // certificate.p12 is the certificate that is going to be used to sign
    var certificatePath = path.join(__dirname, '/../../../resources/certificate.p12');
    var certificateBuffer = fs.readFileSync(certificatePath);
    var signer = new P12Signer(certificateBuffer);
    
    // Once the PDF is ready we need to sign it and eventually store it on disc.
    pdfReady
        .then(function (pdfWithPlaceholder) {
            return signpdf.sign(pdfWithPlaceholder, signer);
        })
        .then(function (signedPdf) {
            var targetPath = path.join(__dirname, '/../output/pdfkit010-with-visual.pdf');
            fs.writeFileSync(targetPath, signedPdf);
        });

    // Finally end the PDFDocument stream.
    pdf.end();
    // This has just triggered the `pdfReady` Promise to be resolved.
};

work();