AVAppGetActiveDoc on Portfolio returns selected pdf not the collection

Hello all.

AVAppGetActiveDoc works fine for single document. It returns me current active AVDoc and then I can copy it to file and then process:

AVDoc pAVDoc = AVAppGetActiveDoc();
PDDoc pDoc = AVDocGetPDDoc(pAVDoc);
PDDocCopyToFile(pDoc, &params);

Portfolio pdf also comes as single pdf file and contains several inside. But unfortunatly AVAppGetActiveDoc does not return a collection object, it returns the one selected in the Porfolio. As the result I can not copy to file the full Portfolio document:

PDDoc pDoc = AVDocGetPDDoc(pAVDoc);
PDCollection pdCollection = PDDocGetPDCollection(pDoc);
PDCollectionIsValid(pdCollection); // FALSE

Is there any way to get the Portfolio object instead of internal pdf one?