Add Digital Signature to an already signed Excel file with JavaScript via C++

Possible Usage Scenarios

Aspose.Cells for JavaScript via C++ provides the Workbook.addDigitalSignature(digitalSignatureCollection) method that you can use to add a digital signature to an already signed Excel file.

Please note while adding a digital signature to an already signed Excel document, if the original document is an Aspose.Cells generated document, it works well. But if the original document is generated by other engines (e.g. Microsoft Excel etc.), Aspose.Cells cannot keep the file the same after loading and re-saving it, which will make the original signature invalid.

How to Add Digital Signature to an Already Signed Excel File

The following sample code demonstrates how to make use of the Workbook.addDigitalSignature(digitalSignatureCollection) method to add a digital signature to an already signed Excel file. Please check the sample Excel file used in this code. This file is already digitally signed. Please check the output Excel file generated by the code. We have used the demo certificate named AsposeDemo.pfx in this code, which has a password aspose. The screenshot shows the effect of the sample code on the sample Excel file after execution.

todo:image_alt_text

Sample Code

<!DOCTYPE html>
<html>
    <head>
        <title>Aspose.Cells Add Digital Signature Example</title>
    </head>
    <body>
        <h1>Add Digital Signature to Workbook</h1>
        <p>Select an Excel file and a PFX certificate, enter the certificate password, then click "Add Digital Signature".</p>
        <input type="file" id="fileInput" accept=".xls,.xlsx" />
        <br/><br/>
        <input type="file" id="certInput" accept=".pfx" />
        <br/><br/>
        <label for="certPassword">Certificate Password:</label>
        <input type="password" id="certPassword" value="aspose" />
        <br/><br/>
        <button id="runExample">Add Digital Signature</button>
        <a id="downloadLink" style="display: none;">Download Result</a>
        <div id="result"></div>

    <script src="aspose.cells.js.min.js"></script>
    <script type="text/javascript">
        const { Workbook, DigitalSignature, DigitalSignatureCollection, SaveFormat, Utils } = AsposeCells;
        
        AsposeCells.onReady({
            license: "/lic/aspose.cells.enc",
            fontPath: "/fonts/",
            fontList: [
                "arial.ttf",
                "NotoSansSC-Regular.ttf"
            ]
        }).then(() => {
            console.log("Aspose.Cells initialized");
        });

        document.getElementById('runExample').addEventListener('click', async () => {
            const fileInput = document.getElementById('fileInput');
            const certInput = document.getElementById('certInput');
            const passwordInput = document.getElementById('certPassword');
            const resultDiv = document.getElementById('result');

            if (!fileInput.files.length) {
                resultDiv.innerHTML = '<p style="color: red;">Please select an Excel file.</p>';
                return;
            }
            if (!certInput.files.length) {
                resultDiv.innerHTML = '<p style="color: red;">Please select a .pfx certificate file.</p>';
                return;
            }

            // Read files as ArrayBuffer
            const excelFile = fileInput.files[0];
            const certFile = certInput.files[0];
            const certPassword = passwordInput.value;

            const excelArrayBuffer = await excelFile.arrayBuffer();
            const certArrayBuffer = await certFile.arrayBuffer();

            // Instantiate Workbook from uploaded Excel file
            const workbook = new Workbook(new Uint8Array(excelArrayBuffer));

            // Create the digital signature collection
            const dsCollection = new DigitalSignatureCollection();

            // Create new digital signature and add it in digital signature collection
            // Using certificate bytes (Uint8Array), password, comment and signing date
            const signature = new DigitalSignature(new Uint8Array(certArrayBuffer), certPassword, "Aspose.Cells added new digital signature in existing digitally signed workbook.", new Date());
            dsCollection.add(signature);

            // Add digital signature collection inside the workbook
            workbook.addDigitalSignature(dsCollection);

            // Save the workbook and provide download link
            const outputData = workbook.save(SaveFormat.Xlsx);
            const blob = new Blob([outputData]);
            const downloadLink = document.getElementById('downloadLink');
            downloadLink.href = URL.createObjectURL(blob);
            downloadLink.download = 'outputDigitallySignedByCells.xlsx';
            downloadLink.style.display = 'block';
            downloadLink.textContent = 'Download Digitally Signed Excel File';

            // Dispose the workbook
            workbook.dispose();

            resultDiv.innerHTML = '<p style="color: green;">Digital signature added successfully! Click the download link to get the signed file.</p>';
        });
    </script>
</html>

Support for XAdES Signature with JavaScript via C++