Bookmarks disappeared after merge of pdf files

I have a solution where i take a random number of pdf files and merge into one file. the source pdf files contains bookmarks but there are no bookmarks in the final pdf file. From the documentation I gather that it should be possible to keep bookmarks?

Yesterday I upgraded the aspose.pdf component to 8.8.0.0 to ensure that I am using the most resent version but that did not change anything.

Am I mistaken when I think it should be possible to keep bookmarks? Is there a limit to the size of the pdf files or…?

Any help would be appreciated.

Below is the code snippet I am using to merge the files so you can see if it is the methodology I am using that is wrong.

Path(s) to pdf files are stored in an array named pdfFiles (as mentioned the number changes all the time)

‘and the files are merged like this:

Dim doc AsNewDocument()

Dim doc1 AsDocument

For i AsInteger = 0 To pdfFiles.Count - 1

    doc1 = NewDocument(pdfFiles(i))

    doc.Pages.Add(doc1.Pages)

Next

‘and the final file is saved:

doc.Save([path where files goes])