var
  input: TStringList;
  output: String;
  I, J: Integer;
begin
  input := TStringList.Create;
  input.Add(ExtractFilePath(ParamStr(0)) + 'Egypt.pdf');
  input.Add(ExtractFilePath(ParamStr(0)) + 'BoraBora.pdf');
  input.Add(ExtractFilePath(ParamStr(0)) + 'London.pdf');

  output := TPath.GetDocumentsPath + '/Merged.pdf';
  TMSFMXNativePDFLib1.BeginDocument(output);
  for I := 0 to input.Count - 1 do
  begin
    TMSFMXNativePDFLib1.OpenDocument(input[I]);
    for J := 1 to TMSFMXNativePDFLib1.GetPageCount do
    begin
      TMSFMXNativePDFLib1.GetPageInfo(J);
      TMSFMXNativePDFLib1.NewPage;
      TMSFMXNativePDFLib1.DrawPage(J);
    end;
    TMSFMXNativePDFLib1.CloseDocument;
  end;
  TMSFMXNativePDFLib1.EndDocument;

  input.Free;
end;