Help with comparing itextsharp with itext7

[Precision999]

Hi

I'm trying to convert some itextsharp stuff to itext7. This itextsharp function just compresses a pdf, replacing the original file as it does so:

Sub compresspdf(myfile As String)

        Dim tempfile As String = Form1.tempfolder & "\temp compress.pdf"

        Dim streamOut As New FileStream(tempfile, FileMode.Create)
        Dim newDoc As Document = New Document(PageSize.A4)
        Dim pdfCopy As PdfSmartCopy = New PdfSmartCopy(newDoc, streamOut)
        pdfCopy.SetMergeFields()
        newDoc.Open()
        Dim pdfTemplate As String = myfile
        Dim pdfReader As New PdfReader(pdfTemplate)
        pdfCopy.AddDocument(pdfReader)
        pdfCopy.Close()
        pdfReader.Close()

        My.Computer.FileSystem.DeleteFile(myfile)
        System.IO.File.Move(tempfile, myfile)

    End Sub

Could anyone give me the equivalent in itext7 please? - I've had a go but it doesn't seem to compress the file the way itextsharp does. If I try to use smartmode I run out of memory, and without that the resulting file does not show any improvement in file size.

EDIT - sorry, should have mentioned I'm running this on a 400mb pdf provided by a client (it's 4000 pages)

Thanks