How to find all internal links in a PDF, using Java Apache PDFBox

I am using the following code (Kotlin) to find hyperlinks in a PDF

    import org.apache.pdfbox.pdmodel.PDDocument
    import org.apache.pdfbox.pdmodel.interactive.action.PDActionURI
    import org.apache.pdfbox.pdmodel.interactive.annotation.PDAnnotationLink
    import ... destination.PDPageXYZDestination
    import java.io.File
    
    fun findAnnotationsTest() {
        val pdfPath = "LinkedPDF.pdf"
        val doc = PDDocument.load(File(pdfPath))
        var pageNo = 0
        for (page in doc.pages) {
            pageNo++
            for (annotation in page.annotations) {
                val subtype = annotation.subtype
                println("Found Annotation ($subtype) on page $pageNo")
                if (annotation is PDAnnotationLink) {
                    val aname = annotation.annotationName
                    println("\t\tfound Link  named $aname on page $pageNo")
                    val link = annotation
                    println("\t\tas string: " + link.toString());
                    println("\t\tdestination: " + link.getDestination());
                    val dest = link.destination
                    val destClass = dest::class
                    println("\t\tdest class is $destClass")
                    if(dest is PDPageXYZDestination){
                        val pageNumber = dest.pageNumber
                        println("\t\tdest page number is $pageNumber")
                    }
    
                    val action = link.action
    
                    if (action == null) {
                        println("\t\tbut action is null")
                        continue
                    }
                    if (action is PDActionURI)
                        println("\t\tURI action is ${action.uri}")
                    else
                        println("\t\tother action is ${action::class}")
                }
                else{
                    println("\tNOT a link")
                }
            }
        }
    }

The input file has hundreds of (working) internal links.

This code finds the annotations and recognizes them as links, but with null PDActions and PDPageXYZDestination's with page number = -1. The output for each link looks like:

    Found Annotation (Link) on page 216
        found Link (Link) named null on page 216
        as string: org.apache.pdfbox....annotation.PDAnnotationLink@3234e239
        destination: org.apache.pdfbox.....destination.PDPageXYZDestination@3d921e20
        dest class is class org.apache.pdfbox...destination.PDPageXYZDestination
        dest page number is -1
        but action is null

BTW, the PDF was created by saving an MS Word document (which had internal links to Word bookmarks) as a PDF.

Any ideas on what I'm doing wrong?

Here's the PDF (a sample): NBSample.pdf

The destination of PDPageDestination is not a number (this is only with external page links), it is a page dictionary, so additional efforts are needed to get the number (the method javadoc mentions this). Here a slightly modified excerpt of the PrintBookmarks.java example:

if (dest instanceof PDPageDestination)
{
    PDPageDestination pd = (PDPageDestination) dest;
    System.out.println("Destination page: " + (pd.retrievePageNumber() + 1));
}