Java PDFBox: Remove the parent element in tagged PDF

I got the Possibly inappropriate use of a "Table" structure element warning in PAC3 validation. Table structure in PDF as follows,

In order to pass the PAC3 I now drag out the tables from the parent tag to an element on its own as like below,

I tried the below code, but it didn't work

PDStructureElement parent=(PDStructureElement)element.getParent();

//parent.setStructureType(StandardStructureTypes.TABLE);
element.insertBefore(element,parent);
element.setParent(parent.getParent());

Please help me with this.

The main issue in the code you show is that you try to insert the element as kid of itself instead of as kid of its current grand parent:

element.insertBefore(element,parent);

You can make it work like this:

if (element instanceof PDStructureElement) {
    PDStructureElement pdStructureElement = (PDStructureElement) element;
    if ("Table".equals(pdStructureElement.getStructureType())) {
        PDStructureNode parentNode = pdStructureElement.getParent();
        if (parentNode instanceof PDStructureElement) {
            PDStructureElement parent = (PDStructureElement) parentNode;
            PDStructureNode newParentNode = parent.getParent();
            if (newParentNode != null) {
                newParentNode.insertBefore(pdStructureElement, parent);
                pdStructureElement.setParent(newParentNode);
                newParentNode.removeKid(parent);
            }
        }
    }
}

(from MoveInStructureTree helper method checkAndMoveTableUp)

Applying this recursively to the structure tree of your PDF removes the Possibly inappropriate use of a "Table" structure element warning in PAC3 validation, cf. the MoveInStructureTree test testMoveTableUpTradeSimple1.

(This code assumes that like in your example document all Table elements are embedded as single kid in a parent element to replace. For other cases you have to add some sanity checks and probably special treatment of other cases.)