''' <summary>
''' Adds PDF document to another PDF document.
''' </summary>
''' <param name="sourcePdfFilename">The name of PDF file, which should be used as source PDF document.</param>
''' <param name="addingPdfFilename">The name of PDF file, which must be added to the initial PDF document.</param>
''' <param name="outputPdfFilename">The name of PDF file, where result PDF document must be saved.</param>
Public Shared Sub AddDocument(sourcePdfFilename As String, addingPdfFilename As String, outputPdfFilename As String)
    ' open source PDF document
    Using document As New Vintasoft.Imaging.Pdf.PdfDocument(sourcePdfFilename)
        ' open adding PDF document
        Using addingDocument As New Vintasoft.Imaging.Pdf.PdfDocument(addingPdfFilename)
            ' create an instance of PdfDocumentCopyCommand class and specify the source PDF document for PdfDocumentCopyCommand
            Dim copyDocument As New Vintasoft.Imaging.Pdf.Processing.PdfDocumentCopyCommand(document)

            ' specify that PdfDocumentCopyCommand must copy bookmarks from adding PDF document to the source PDF document
            copyDocument.CopyBookmarks = True
            ' specify that PdfDocumentCopyCommand must copy document-level JavaScript code from adding PDF document to the source PDF document
            copyDocument.CopyDocumentLevelJavaScripts = True
            ' specify that PdfDocumentCopyCommand must copy interactive form from adding PDF document to the source PDF document
            copyDocument.CopyInteractiveForm = True

            ' copy adding PDF document to the input PDF document
            copyDocument.Execute(addingDocument)

            ' if output path is not specified
            If String.IsNullOrEmpty(outputPdfFilename) Then
                ' save result PDF document to the source file
                document.SaveChanges()
            Else
                ' if output path is specified
                ' save result PDF document to the output file
                document.SaveChanges(outputPdfFilename)
            End If
        End Using
    End Using
End Sub

/// <summary>
/// Adds PDF document to another PDF document.
/// </summary>
/// <param name="sourcePdfFilename">The name of PDF file, which should be used as source PDF document.</param>
/// <param name="addingPdfFilename">The name of PDF file, which must be added to the initial PDF document.</param>
/// <param name="outputPdfFilename">The name of PDF file, where result PDF document must be saved.</param>
public static void AddDocument(string sourcePdfFilename, string addingPdfFilename, string outputPdfFilename)
{
    // open source PDF document
    using (Vintasoft.Imaging.Pdf.PdfDocument document = new Vintasoft.Imaging.Pdf.PdfDocument(sourcePdfFilename))
    {
        // open adding PDF document
        using (Vintasoft.Imaging.Pdf.PdfDocument addingDocument = new Vintasoft.Imaging.Pdf.PdfDocument(addingPdfFilename))
        {
            // create an instance of PdfDocumentCopyCommand class and specify the source PDF document for PdfDocumentCopyCommand
            Vintasoft.Imaging.Pdf.Processing.PdfDocumentCopyCommand copyDocument =
                new Vintasoft.Imaging.Pdf.Processing.PdfDocumentCopyCommand(document);

            // specify that PdfDocumentCopyCommand must copy bookmarks from adding PDF document to the source PDF document
            copyDocument.CopyBookmarks = true;
            // specify that PdfDocumentCopyCommand must copy document-level JavaScript code from adding PDF document to the source PDF document
            copyDocument.CopyDocumentLevelJavaScripts = true;
            // specify that PdfDocumentCopyCommand must copy interactive form from adding PDF document to the source PDF document
            copyDocument.CopyInteractiveForm = true;

            // copy adding PDF document to the input PDF document
            copyDocument.Execute(addingDocument);

            // if output path is not specified
            if (string.IsNullOrEmpty(outputPdfFilename))
            {
                // save result PDF document to the source file
                document.SaveChanges();
            }
            // if output path is specified
            else
            {
                // save result PDF document to the output file
                document.SaveChanges(outputPdfFilename);
            }
        }
    }
}