The sample demonstrates how to merge multiple PDF documents to one PDF document.

(NO screenshot)

using System;
using Spire.Pdf;

namespace MergeDocuments
{
    class Program
    {
        static void Main(string[] args)
        {
            //pdf document list
            String[] files = new String[]
            {
                @"Sample3.pdf",
                @"Sample2.pdf",
                @"Sample1.pdf"
            };
            //open pdf documents            
            PdfDocument[] docs = new PdfDocument[files.Length];
            for (int i = 0; i < files.Length; i++)
            {
                docs[i] = new PdfDocument(files[i]);
            }

            //append document
            docs[0].AppendPage(docs[1]);

            //import page
            for (int i = 0; i < docs[2].Pages.Count; i = i + 2)
            {
                docs[0].InsertPage(docs[2], i);
            }

            //Save pdf file.
            docs[0].SaveToFile("MergeDocuments.pdf");

            //close
            foreach (PdfDocument doc in docs)
            {
                doc.Close();
            }

            //Launching the Pdf file.
            System.Diagnostics.Process.Start("MergeDocuments.pdf");
        }
    }
}

Imports Spire.Pdf

Namespace MergeDocuments
    Friend Class Program
        Shared Sub Main(ByVal args() As String)
            'pdf document list
            Dim files() As String = {"Sample3.pdf", "Sample2.pdf", "Sample1.pdf"}
            'open pdf documents            
            Dim docs(files.Length - 1) As PdfDocument
            For i As Integer = 0 To files.Length - 1
                docs(i) = New PdfDocument(files(i))
            Next i

            'append document
            docs(0).AppendPage(docs(1))

            'import page
            For i As Integer = 0 To docs(2).Pages.Count - 1 Step 2
                docs(0).InsertPage(docs(2), i)
            Next i

            'Save pdf file.
            docs(0).SaveToFile("MergeDocuments.pdf")

            'close
            For Each doc As PdfDocument In docs
                doc.Close()
            Next doc

            'Launching the Pdf file.
            Process.Start("MergeDocuments.pdf")
        End Sub

    End Class
End Namespace

The sample demonstrates how to merge two documents.

private void button1_Click(object sender, EventArgs e)
{
    string fileName = OpenFile();
    string fileMerge = OpenFile();
    if ((!string.IsNullOrEmpty(fileName)) && (!string.IsNullOrEmpty(fileMerge)))
    {
        //Create word document
        Document document = new Document();
        document.LoadFromFile(fileName,FileFormat.Doc);

        Document documentMerge = new Document();
        documentMerge.LoadFromFile(fileMerge, FileFormat.Doc);

        foreach( Section sec in documentMerge.Sections)
        {
            document.Sections.Add(sec.Clone());
        }

        //Save doc file.
        document.SaveToFile("Sample.doc", FileFormat.Doc);

        //Launching the MS Word file.
        WordDocViewer("Sample.doc");
    }


}

private string OpenFile()
{
    openFileDialog1.Filter = "Word Document (*.doc)|*.doc";
    openFileDialog1.Title = "Choose a document to merage";

    openFileDialog1.RestoreDirectory = true;
    if (openFileDialog1.ShowDialog() == DialogResult.OK)
    {
        return openFileDialog1.FileName;
    }

    return string.Empty;
}

private void WordDocViewer(string fileName)
{
    try
    {
        System.Diagnostics.Process.Start(fileName);
    }
    catch { }
}

Private Sub button1_Click(ByVal sender As Object, ByVal e As EventArgs) Handles button1.Click
	Dim fileName As String = OpenFile()
	Dim fileMerge As String = OpenFile()
	If ((Not String.IsNullOrEmpty(fileName))) AndAlso ((Not String.IsNullOrEmpty(fileMerge))) Then
		'Create word document
		Dim document_Renamed As New Document()
		document_Renamed.LoadFromFile(fileName,FileFormat.Doc)

		Dim documentMerge As New Document()
		documentMerge.LoadFromFile(fileMerge, FileFormat.Doc)

		For Each sec As Section In documentMerge.Sections
			document_Renamed.Sections.Add(sec.Clone())
		Next sec

		'Save doc file.
		document_Renamed.SaveToFile("Sample.doc", FileFormat.Doc)

		'Launching the MS Word file.
		WordDocViewer("Sample.doc")
	End If


End Sub

Private Function OpenFile() As String
	openFileDialog1.Filter = "Word Document (*.doc)|*.doc"
	openFileDialog1.Title = "Choose a document to merage"

	openFileDialog1.RestoreDirectory = True
	If openFileDialog1.ShowDialog() = DialogResult.OK Then
		Return openFileDialog1.FileName
	End If

	Return String.Empty
End Function

Private Sub WordDocViewer(ByVal fileName As String)
	Try
		Process.Start(fileName)
	Catch
	End Try
End Sub

The sample demonstrates how to merge nestedmail into a document.

private void button1_Click(object sender, EventArgs e)
{
    List list = new List();
    DataSet dsData = new DataSet();

    dsData.ReadXml(@"..\..\..\..\..\..\Data\Orders.xml");

    //Create word document
    Document document = new Document();
    document.LoadFromFile(@"..\..\..\..\..\..\Data\Invoice.doc");

    DictionaryEntry dictionaryEntry = new DictionaryEntry("Customer", string.Empty);
    list.Add(dictionaryEntry);

    dictionaryEntry = new DictionaryEntry("Order", "Customer_Id = %Customer.Customer_Id%");
    list.Add(dictionaryEntry);

    document.MailMerge.ExecuteWidthNestedRegion(dsData, list);
  
    //Save doc file.
    document.SaveToFile("Sample.doc", FileFormat.Doc);

    //Launching the MS Word file.
    WordDocViewer("Sample.doc");
}

private void WordDocViewer(string fileName)
{
    try
    {
        System.Diagnostics.Process.Start(fileName);
    }
    catch { }
}

Private Sub button1_Click(ByVal sender As Object, ByVal e As EventArgs) Handles button1.Click
	Dim list_Renamed As New List(Of DictionaryEntry)()
	Dim dsData As New DataSet()

	dsData.ReadXml("..\..\..\..\..\..\Data\Orders.xml")

	'Create word document
	Dim document_Renamed As New Document()
	document_Renamed.LoadFromFile("..\..\..\..\..\..\Data\Invoice.doc")

	Dim dictionaryEntry_Renamed As New DictionaryEntry("Customer", String.Empty)
	list_Renamed.Add(dictionaryEntry_Renamed)

	dictionaryEntry_Renamed = New DictionaryEntry("Order", "Customer_Id = %Customer.Customer_Id%")
	list_Renamed.Add(dictionaryEntry_Renamed)

	document_Renamed.MailMerge.ExecuteWidthNestedRegion(dsData, list_Renamed)

	'Save doc file.
	document_Renamed.SaveToFile("Sample.doc", FileFormat.Doc)

	'Launching the MS Word file.
	WordDocViewer("Sample.doc")
End Sub

Private Sub WordDocViewer(ByVal fileName As String)
	Try
		Process.Start(fileName)
	Catch
	End Try
End Sub

The sample demonstrates how to merge mail into a document.

private void button1_Click(object sender, EventArgs e)
{
    //Create word document
    Document document = new Document();
    document.LoadFromFile(@"..\..\..\..\..\..\Data\Fax.doc");

    string[] filedNames = new string[]{"Contact Name","Fax","Date"};

    string[] filedValues = new string[]{"John Smith","+1 (69) 123456",System.DateTime.Now.Date.ToString()};

    document.MailMerge.Execute(filedNames, filedValues);

  
    //Save doc file.
    document.SaveToFile("Sample.doc", FileFormat.Doc);

    //Launching the MS Word file.
    WordDocViewer("Sample.doc");
}

private void WordDocViewer(string fileName)
{
    try
    {
        System.Diagnostics.Process.Start(fileName);
    }
    catch { }
}

Private Sub button1_Click(ByVal sender As Object, ByVal e As EventArgs) Handles button1.Click
	'Create word document
	Dim document_Renamed As New Document()
	document_Renamed.LoadFromFile("..\..\..\..\..\..\Data\Fax.doc")

	Dim filedNames() As String = {"Contact Name","Fax","Date"}

	Dim filedValues() As String = {"John Smith","+1 (69) 123456",Date.Now.Date.ToString()}

	document_Renamed.MailMerge.Execute(filedNames, filedValues)


	'Save doc file.
	document_Renamed.SaveToFile("Sample.doc", FileFormat.Doc)

	'Launching the MS Word file.
	WordDocViewer("Sample.doc")
End Sub

Private Sub WordDocViewer(ByVal fileName As String)
	Try
		Process.Start(fileName)
	Catch
	End Try
End Sub