MemoryStream ms1 = new MemoryStream();

using (ZipArchive archive = new ZipArchive(ms1, ZipArchiveMode.Create, false, null))
{
	using (PdfFileSource fileSource = new PdfFileSource(File.OpenRead(documentToSplit)))
	{
		string splitDocumentName = "1st page.pdf";
		using (ZipArchiveEntry entry = archive.CreateEntry(splitDocumentName))
		{
			using (PdfStreamWriter writer = new PdfStreamWriter(entry.Open()))
			{
				PdfPageSource page = fileSource.Pages[0];
				writer.WritePage(page);
			}
		}
	}
}

File.WriteAllBytes("exported.zip", ms1.ToArray());

using (var archive = new ZipArchive(stream, ZipArchiveMode.Create, false, null))
    {
        foreach (var item in array)
        {
            using (var entry = archive.CreateEntry($"{item.Name}.reg-ext"))
            {
                XmlInOut<RegulationItem>.SaveToStream(entry.Open(), item);
            }
        }
    }

    Sub Main()
        Dim sZipFilePath As String = "..\..\test.zip"
        File.Delete(sZipFilePath)

        CreateArchive(sZipFilePath)

        Dim decryptionSettings As DecryptionSettings = EncryptionSettings.CreateDecryptionSettings()
        AddHandler decryptionSettings.PasswordRequired, AddressOf DecryptionSettings_PasswordRequired
        Dim compressionSettings As CompressionSettings = Nothing
        Dim encoding As Encoding = Nothing
        Using oFS As FileStream = File.Open(sZipFilePath, FileMode.OpenOrCreate)


            Using oArchive As ZipArchive = ZipArchive.Update(oFS, encoding, compressionSettings, decryptionSettings)
                For Each entry As ZipArchiveEntry In oArchive.Entries
                    Using entryStream As Stream = entry.Open()
                        Dim reader As New StreamReader(entryStream)
                        Dim content As String = reader.ReadToEnd()

                        entryStream.Seek(0, SeekOrigin.End)
                        Dim writer As New StreamWriter(entryStream)
                        writer.WriteLine("Updated line.")
                        writer.Flush()
                    End Using
                Next
            End Using
        End Using
    End Sub

    Private Sub CreateArchive(sZipFilePath As String)
        Using stream As Stream = File.Open(sZipFilePath, FileMode.Create)
            Dim encryptionSettings As PasswordEncryptionSettings = encryptionSettings.CreatePkzipPasswordEncryptionSettings()
            encryptionSettings.Password = "MyPassword"
            Dim compressionSettings As CompressionSettings = Nothing
            Dim encoding As Encoding = Nothing

            Using archive As ZipArchive = ZipArchive.Create(stream, encoding, compressionSettings, encryptionSettings)

                Using entry As ZipArchiveEntry = archive.CreateEntry("text.txt")
                    Dim writer As StreamWriter = New StreamWriter(entry.Open())
                    writer.WriteLine("Hello world!")
                    writer.Flush()
                End Using
            End Using
        End Using
    End Sub

    Private Sub DecryptionSettings_PasswordRequired(ByVal sender As Object, ByVal e As PasswordRequiredEventArgs)
        e.Password = "MyPassword"
    End Sub

Imports System.IO
Imports System.Text
Imports Telerik.Windows.Zip

Module Module1

    Sub Main()
        Dim sZipFilePath As String = "..\..\test.zip"
        File.Delete(sZipFilePath)

        CreateArchive(sZipFilePath)

        Dim decryptionSettings As DecryptionSettings = EncryptionSettings.CreateDecryptionSettings()
        AddHandler decryptionSettings.PasswordRequired, AddressOf DecryptionSettings_PasswordRequired
        Dim compressionSettings As CompressionSettings = Nothing
        Dim encoding As Encoding = Nothing
        Using oFS As FileStream = File.Open(sZipFilePath, FileMode.OpenOrCreate)


            Using oArchive As ZipArchive = ZipArchive.Update(oFS, encoding, compressionSettings, decryptionSettings)
                For Each entry As ZipArchiveEntry In oArchive.Entries
                    Using entryStream As Stream = entry.Open()
                        Dim reader As New StreamReader(entryStream)
                        Dim content As String = reader.ReadToEnd()

                        entryStream.Seek(0, SeekOrigin.End)
                        Dim writer As New StreamWriter(entryStream)
                        writer.WriteLine("Updated line.")
                        writer.Flush()
                    End Using
                Next
            End Using
        End Using
    End Sub

    Private Sub CreateArchive(sZipFilePath As String)
        Using stream As Stream = File.Open(sZipFilePath, FileMode.Create)
            Dim encryptionSettings As PasswordEncryptionSettings = encryptionSettings.CreatePkzipPasswordEncryptionSettings()
            encryptionSettings.Password = "MyPassword"
            Dim compressionSettings As CompressionSettings = Nothing
            Dim encoding As Encoding = Nothing

            Using archive As ZipArchive = ZipArchive.Create(stream, encoding, compressionSettings, encryptionSettings)

                Using entry As ZipArchiveEntry = archive.CreateEntry("text.txt")
                    Dim writer As StreamWriter = New StreamWriter(entry.Open())
                    writer.WriteLine("Hello world!")
                    writer.Flush()
                End Using
            End Using
        End Using
    End Sub

    Private Sub DecryptionSettings_PasswordRequired(ByVal sender As Object, ByVal e As PasswordRequiredEventArgs)
        e.Password = "MyPassword"
    End Sub

End Module