使用以下功能檢測已簽名的 PDF 是否被修改過

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在對(duì) PDF 文檔進(jìn)行數(shù)字簽名后，該 PDF 已被鎖定以防止更改或允許檢測更改。本文將介紹如何使用 Spire.PDF 檢測已簽名的 PDF 是否被修改。

為了測試此功能，我們創(chuàng)建了一個(gè) PDF 文檔，并使用數(shù)字簽名對(duì) PDF 進(jìn)行了簽名，然后將示例文檔中的 "PDF "改為 "Pdf"，并保存為另一個(gè)文件。下面是修改后的 PDF 文檔：

代碼片段

步驟 1：創(chuàng)建 Window Forms 應(yīng)用程序并設(shè)計(jì) form1 如下。

第 2 步：雙擊 'Load' 按鈕，編寫以下代碼，以便從文件夾中查找 PDF 文件，并在 textBox1.Text 中返回文件路徑。

private void btnLoad_Click(object sender, EventArgs e)
{
    OpenFileDialog fileName = new OpenFileDialog();
    fileName.InitialDirectory = Application.StartupPath;
    fileName.Filter = "All files|*.pdf";
    if (fileName.ShowDialog() == DialogResult.OK)
    {
        string Path = fileName.FileName.ToString();
        textBox1.Text = Path;
    }
}

第3步：在 'Check'.按鈕上輸入以下代碼。在這一部分，我們獲取PDF文檔中的所有簽名，然后調(diào)用PdfSignature.VerifyDocModified()方法檢測文檔是否在簽名后被修改。如果被修改則返回true，否則返回false。

private void btnCheck_Click(object sender, EventArgs e)
{
    //get signatures from PDF
    List signatures = new List();
    using (PdfDocument pdf = new PdfDocument(textBox1.Text))
    {
        PdfFormWidget form = pdf.Form as PdfFormWidget;
        for (int i = 0; i < form.FieldsWidget.Count; i++)
        {
            PdfSignatureFieldWidget field = form.FieldsWidget[i] as PdfSignatureFieldWidget;
            if (field != null && field.Signature != null)
            {
                PdfSignature signature = field.Signature;
                signatures.Add(signature);
            }
        }
        PdfSignature signatureOne = signatures[0];
        //detect if the PDF was modified
        bool modified = signatureOne.VerifyDocModified();
        if (modified == true)
        {
            MessageBox.Show("The document was modified");
        }
    }
}

運(yùn)行程序并加載修改后的文檔，點(diǎn)擊  'Check'按鈕后會(huì)得到以下輸出結(jié)果。

完整代碼：

private void btnLoad_Click(object sender, EventArgs e)
{
    OpenFileDialog fileName = new OpenFileDialog();
    fileName.InitialDirectory = Application.StartupPath;
    fileName.Filter = "All files|*.pdf";
    if (fileName.ShowDialog() == DialogResult.OK)
    {
        string Path = fileName.FileName.ToString();
        textBox1.Text = Path;
    }
}
private void btnCheck_Click(object sender, EventArgs e)
{
    //get signatures from PDF
    List signatures = new List();
    using (PdfDocument pdf = new PdfDocument(textBox1.Text))
    {
        PdfFormWidget form = pdf.Form as PdfFormWidget;
        for (int i = 0; i < form.FieldsWidget.Count; i++)
        {
            PdfSignatureFieldWidget field = form.FieldsWidget[i] as PdfSignatureFieldWidget;
            if (field != null && field.Signature != null)
            {
                PdfSignature signature = field.Signature;
                signatures.Add(signature);
            }
        }
        PdfSignature signatureOne = signatures[0];
        //detect if the PDF was modified
        bool modified = signatureOne.VerifyDocModified();
        if (modified == true)
        {
            MessageBox.Show("The document was modified");
        }
    }
}