/// <summary>
/// Converts standard TIFF file to a big TIFF file (TIFF file which can be bigger than 4Gb).
/// </summary>
public void ConvertTiffToBigTiff(string tiffFileName, string bigTiffFileName)
{
    // open standard TIFF file
    using (Vintasoft.Imaging.Codecs.ImageFiles.Tiff.TiffFile tiffFile = 
        new Vintasoft.Imaging.Codecs.ImageFiles.Tiff.TiffFile(tiffFileName))
    {
        // create big TiffFile
        using (Vintasoft.Imaging.Codecs.ImageFiles.Tiff.TiffFile bigTiffFile = 
            new Vintasoft.Imaging.Codecs.ImageFiles.Tiff.TiffFile(
                Vintasoft.Imaging.Codecs.ImageFiles.Tiff.TiffFileFormat.LittleEndian, 
                Vintasoft.Imaging.Codecs.ImageFiles.Tiff.TiffFileVersion.BigTIFF))
        {
            // for each page of standard TIFF file
            foreach (Vintasoft.Imaging.Codecs.ImageFiles.Tiff.TiffPage page in tiffFile.Pages)
                // add page to a big TIFF file
                bigTiffFile.Pages.Add(page);

            // save big TIFF file to a disk
            bigTiffFile.Save(bigTiffFileName);
        }
    }
}

''' <summary>
''' Converts standard TIFF file to a big TIFF file (TIFF file which can be bigger than 4Gb).
''' </summary>
Public Sub ConvertTiffToBigTiff(tiffFileName As String, bigTiffFileName As String)
    ' open standard TIFF file
    Using tiffFile As New Vintasoft.Imaging.Codecs.ImageFiles.Tiff.TiffFile(tiffFileName)
        ' create big TiffFile
        Using bigTiffFile As New Vintasoft.Imaging.Codecs.ImageFiles.Tiff.TiffFile(Vintasoft.Imaging.Codecs.ImageFiles.Tiff.TiffFileFormat.LittleEndian, Vintasoft.Imaging.Codecs.ImageFiles.Tiff.TiffFileVersion.BigTIFF)
            ' for each page of standard TIFF file
            For Each page As Vintasoft.Imaging.Codecs.ImageFiles.Tiff.TiffPage In tiffFile.Pages
                ' add page to a big TIFF file
                bigTiffFile.Pages.Add(page)
            Next

            ' save big TIFF file to a disk
            bigTiffFile.Save(bigTiffFileName)
        End Using
    End Using
End Sub